E  STUDY  OF 


ECTRIC  MOTORS 


THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

LOS  ANGELES 

GIFT  OF 
R.   E.   Hopkins 


The  Study  of  Electric 
Motors  by  Experiment 


CONTAINING 

Sixty  Experiments  that  Bear  Directly  upon  the  Con- 
struction, Operation  and  Explanation  of  Electric 
Motors ;  together  ivith  Much  Helpful  Information 
upon  the  Experimental  c/lpparatus  Required 


By 
THOMAS  M.  ST.  JOHN,  Met.  E. 

Author  of  "Fun  with  Electricity,"  "The  Study  of  Elementary 
Electricity  and  Magnetism  by  Experiment,"  "Wireless 
Telegraphy  for  Amateurs  and  Students,"  "Elec- 
trical Handicraft,"  "Things  a  Boy  Should 
Know  About  Electricity,"  Etc.,  Etc. 


New  York 

THOMAS  M.  ST.  JOHN 
PUBLISHER 


COPYRIGHT,   1910,   BY  THOMAS  M.    ST.   JOHN 


BY  THE  SAME  AUTHOR—  (Taniai  L 


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Games.  Puzzles  and  Educational  Amusements 

Catalogue   \7pon  Application 

THOMAS  M.  St.  JOHN,  848  Ninth  Ave.,  N.  Y. 


s 


THE    STUDY    OF     ELECTRIC 
MOTORS  BY  EXPERIMENT 


TABLE  OF  CONTENTS 

PAGE 

CHAPTER  I.    Materials  of  Construction 9 

Laboratory  Motors  and  Dynamos. — Materials  of  Con- 
struction. —  Iron.  —  Copper.  —  Permanent  Magnets. 
— Electromagnets. 

CHAPTER  II.    Permanent  Magnetism  12 

Exp.  1,  To  study  the  horseshoe  magnet. — Exp.  2,  To 
see  what  ordinary  things  are  acted  upon  by  a  mag- 
net.— Magnetism. — Exp.  3,  To  find  through  what  sub- 
stances magnetism  will  act. — Exp.  4,  Making  mag- 
nets from  a  magnet. — Exp.  5,  To  see  what  is  meant 
by  the  north  pole  of  a  magnet. — Exp.  6,  Attractions 
and  repulsions  of  magnets. — Exp.  7,  To  see  if  we 
can  make  more  than  two  poles  in  a  bar  magnet. — 
Exp.  8,  To  study  the  theory  of  magnetism. — Exp.  9, 
To  find  whether  soft  iron  will  permanently  retain 
magnetism. — Exp.  10,  Hard  steel  and  soft  steel. — 
Exp.  11,  About  residual  magnetism. — Exp.  12,  About 
induced  magnetism. — Exp.  13,  About  polarization  and 
pole-pieces. — Exp.  14,  To  study  combinations  of  pole- 
pieces. — Exp.  IS,  To  study  the  effect  of  a  continuous 
pole-piece. — Exp.  16,  To  study  the  magnetic  field  of 
the  horseshoe  magnet. — Exp.  17,  Magnetic  field  with 
armature  in  place. — Exp.  18,  Lines  of  force  and  air- 
gaps. — Exp.  19,  Hollow  Armatures. — Exp.  20,  To  Study 
a  certain  combination  of  two  magnets. 

CHAPTER  III.    Experimental  Apparatus 28 

Experimental  Apparatus. — Strap  Key,  Style  A. — Strap 
Key,  Style  B.— Strap  Key  with  Side  Switch.— Double- 


VI  TABLE   OF   CONTENTS 

PAGE 

Key  Current-Reverser. — How  this  Reverser  Works. 
—Two-Point  Switch.— Rheostats.— Five-Point  Rheo- 
stat.— Eleven-Point  Rheostat. — Current  Detectors. — 
Simple  Current  Detector. — Handy  Current  Detector. 

CHAPTER  IV.     Electromagnetism 38 

Exp.  21,  Electric  current  and  magnetic  needle. — Exp. 
22,  Reversing  the  current  in  the  detector. — Exp.  23, 
Magnetism  from  hollow  coils  of  wire. — Exp.  24,  About 
coils  of  wire  with  cores. — Exp.  25,  Polarity  of  coils. 
— Exp.  26,  About  horseshoe  electromagnets. — Exp. 

27,  Regarding  the  joining  of  electromagnets. — Exp. 

28,  Magnetic  figure  of  electromagnets. — Exp.  29,  Mag- 
netic figure  of  single  electromagnets. — Exp.  30,  Mag- 
netic figure  of  two  like  poles. 

CHAPTER  V.    Motion  and  Currents 46 

Exp.  31,  Motion  produced  with  a  hollow  coil  of  wire 
and  a  piece  of  soft  iron. — Exp.  32,  Motion  produced 
with  a  hollow  coil  of  wire  and  a  bar  magnet. — Exp. 
33,  Motion  produced  with  an  electromagnet  and  a 
piece  of  iron. — Exp.  34,  Motion  with  an  electromag- 
net and  a  bar  magnet. — Exp.  35,  Motion  with  an 
electromagnet  and  a  horseshoe  magnet. — Exp.  36, 
Motion  with  two  electromagnets. — Exp.  37,  Rotary 
motion  with  a  hollow  coil  and  a  permanent  magnet. 
— Exp.  38,  Rotary  motion  with  a  permanent  magnet 
and  an  electromagnet. 

CHAPTER  VI.    Electric  Motors  in  General 50 

Simple  Action  of  Motors. — The  Field-Magnets. — Ar- 
matures.— Commutators. — The  Brushes. — Methods  of 
Winding. — Reversing  Motors. — Coils  in  ^'Series."— 
Coils  in  "Shunt." 

CHAPTER  VII.  Practical  Experiments  with  Motors. . .  55 
Small  Motors. — Motor  No.  1. — Taking  Motor  No.  1 
Apart. — Exp.  39,  To  test  the  poles  of  the  field-mag- 
nets.— Exp.  40,  To  test  for  residual  magnetism  in  the 
pole-pieces. — Exp.  41,  To  test  the  lifting-power  of  the 
field-magnets. — Exp.  42,  To  test  the  lifting-power  of 
the  field-magnets  when  the  armature  is  in  place. — 


TABLE   OF    CONTENTS  VII 

PAGE 

Exp.  43,  To  study  the  magnetic  field  of  the  field-mag- 
nets with  the  armature  in  place. — Exp.  44,  To  test  the 
magnetic  field  of  the  field-magnets  with  the  armature 
removed. — Exp.  45,  Making  permanent  magnets  with 
the  motor. — Exp.  46,  To  test  the  armature  for  mag- 
netism.— Exp.  47,  To  test  the  armature-magnets  for 
poles. 

CHAPTER  VIII.     Speed  Regulation  and  Direction  of 

Rotation 64 

Exp.  48,  Direction  of  Rotation. — Attractions  and  Re- 
pulsions in  Motor  No.  1. — Exp.  49,  Backward  motion 
for  Motor  No.  1. — Exp.  50,  Reversing  Motor  No.  1 
with  the  current-reverser. — Exp.  51,  Reversing  Motor 
No.  1  by  a  second  method. — Exp.  52,  Regulation  of 
speed  for  Motor  No.  1,  coils  in  series. — Exp.  53,  Con- 
trolling speed  and  direction  of  rotation  of  Motor  No. 
1,  series-wound. — Load  on  Motors. — Series-Wound 
Motors. — Exp.  54,  Motor  No.  1,  shunt-wound. — Exp. 
55,  Motor  No.  1,  shunt-wound  and  reversible,  with 
one  method  of  speed  regulation. — Exp.  56,  Motor  No. 
1,  shunt-wound  and  reversible,  with  a  second  method 
of  speed  control. — Direct-Current  Shunt- Wound  Mo- 
tors.— Regulation  of  Field-Magnetism. — Exp.  57,  Mo- 
tor No.  1,  shunt-wound  and  reversible,  with  speed 
control  by  regulation  of  field-magnetism,  together 
with  starting-box. — Starting-Boxes. — Exp.  58,  Coun- 
ter-Electromotive force  of  motors. — Counter- Electro- 
motive force. — Exp.  59,  To  show  in  which  direction 
the  counter-current  flows  in  a  motor. — Exp.  60,  Regu- 
lation of  speed  with  lamps  in  parallel. 

CHAPTER  IX.    Various  Electric  Motors 86 

Small  Motors  and  Large  Motors. — Compound- Wound 
Motors. — Comparison  of  Series,  Shunt  and  Com- 
pound Motors.  —  Differentially- Wound  Motors. — 
Alternating-Current  Motors.  —  Railway  Motors. — 
Special  Motors. — Protection  of  Motors. — Motor  No. 
2. — Dynamo-Motor  No.  3. — 110- Volt  Motors. — Motors 
for  Intermittent  Duty. — 110-Volt  Laboratory  Motors. 
— A  One-Eighth  Horse-Power  Motor. — A  One- 


Vlll  TABLE   OF   CONTENTS 

PAGE 

Seventh  Horse-Power  Motor. — Another  One-Seventh 
Horse-Power   Motor. — A   One-Quarter  Horse-Power 
^lotor. — A  One-Tenth  Horse-Power  Motor. 
CHAPTER  X.    Electric  Current  for  Running  Motors...   101 
Various    Methods. — Battery   Currents. — Forcing   Dry 
Batteries. — Arrangement  of  Cells. — Storage-Batteries. 
Running  Small  Motors  from  Small  Dynamos. — Bank 
of  Lamps. — Battery  Regulator  for  110- Volt  Currents. 


THE    STUDY    OF    ELECTRIC 
MOTORS  BY  EXPERIMENT 

CHAPTER  I 
MATERIALS  OF  CONSTRUCTION 

1.  Laboratory  Motors  and  Dynamos.  When  the  stu- 
dent gets  to  the  point  where  he  begins  his  experiments 
with  motors,  he  feels  that  he  is  doing  something,  for 
things  begin  to  move  and  he  can  see  that  he  is  pro- 
ducing results  right  from  the  start.  There  are  many 
things  that  can  be  done  with  a  properly-constructed 
motor,  and  a  motor  that  will  merely  go  around  is  a  very 
poor  sort  of  a  thing  for  the  student;  in  fact,  it  isn't 
worth  anything  to  use  in  the  laboratory.  What  the 
student  needs  is  a  motor  that  can  be  taken  apart  and 
used  for  experiments,  one  that  is  so  constructed  that  it 
shows  how  the  big  machines  work,  and  one  that  is 
under  perfect  control.  Motors  should  be  easily  controlled 
as  to  speed,  as  well  as  to  the  direction  of  rotation. 

The  advantage  of  the  laboratory  motors  described  in 
this  book  is  that  they  will  do  all  that  other  motors  will 
do,  and  much  besides;  for  they  are  designed  especially 
for  those  who  want  to  use  them  for  experimental  pur- 
poses as  a  part  of  the  general  study  of  electricity. 

As  the  main  features  and  parts  of  small  dynamos  and 
motors  are  the  same — in  fact,  most  small  dynamos  can 


10  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

be  used  as  motors — we  shall  first  take  up  a  few  experi- 
ments that  will  aid  in  understanding  both  machines.  The 
student  will  find  it  to  his  advantage  to  perform  the  ex- 
periments that  are  herein  suggested,  unless  he  has  already 
done  so,  for  it  will  make  things  clear  as  he  goes  along. 

2.  Materials  of  Construction.     It  would  seem  that  big 
motors  or  dynamos  should  be  built  of  many  different 
things  and  be  very  complicated  in  order  to  be  able  to  do 
what  is  expected  of  them;  but  when  you  examine  them 
you    see,   on   the   contrary,   that   they   are   very   simple 
in  construction  and  that  they  are  made  up  chiefly  of  but 
two  metals,  iron  and  copper.    Of  course,  there  are  other 
things   on   them,   such   as   insulating   materials,   nickel- 
plating,  etc.,  but  these  are  there  chiefly  for  looks  and  for 
keeping  the  iron  and  copper  in  place  so  that  they  can  do 
their  proper  work. 

There  must  be  some  reason  for  this  choice  of  materials 
and  for  this  simplicity  of  construction,  and  that  is  what 
we  want  to  find  out  by  experiment.  If  the  student  will 
keep  these  two  things  in  mind,  when  doing  the  experi- 
ments, he  will  see  why  these  special  experiments  and 
explanations  have  been  given. 

3.  Iron  is  an  element,  from  a  chemical  standpoint,  but 
we  seldom  see  pure  iron.     About  all  of  the  iron  we  use 
and  that  is  sold  in  the  market  for  wagons,  machinery, 
bridges,   etc.,    is    far    from   being   pure,   as   it   contains 
other  things,  too,  such  as  carbon,  phosphorus,  silicon,  sul- 
phur, etc.     These  impurities,  as  the  chemist  calls  them, 
are  the  very  things  that  make  it  possible  to  so  modify 
the  iron  that  it  becomes  suitable  for  electrical  purposes; 
for,  if  we  had  only  the  absolutely  pure  iron,  we  could 
not  have  steel  and  other  forms  of  iron  that  are  really 
more  important  than  the  pure  iron.     We  shall  see  how 
iron  is  used  in  the  construction  of  these  wonderful  elec- 


MATERIALS   OF    CONSTRUCTION  II 

trical  machines,  and  find  out  why  certain  kinds  of  iron 
are  better  than  others  for  the  purpose. 

4.  Copper  is  also  an  element  used  in  electrical  ma- 
chines, but  in  this  case  we  try  to  get  it  as  pure  as  pos- 
sible.    The  copper  used  for  the  wire  and  other  parts  of 
motors  and  dynamos  must  be  pure,  and  a  great  deal  of 
care  is  used  in  making  it  for  these  purposes.     The  ex- 
periments that  follow  will  show  how  the  copper  wire  and 
iron  act  together  to  make  the  motor  or  dynamo  a  suc- 
cess. 

5.  Permanent   Magnets.     About   the   first   thing  we 
think  of  when  the  magnet  is  suggested,  is  the  ordinary 
horseshoe  magnet.    These  have  been  made  for  centuries, 
but  it  took  a  long  time  before  the  connection  between 
electricity  and  magnetism  .was  discovered.     The  horse- 
shoe magnet  is  a  permanent  magnet,  for  it  holds  its  mag- 
netism for  years  if  handled  properly. 

6.  Electromagnets  are  those  produced  with  the  aid  of 
the  electric  current,  and  it  is  these  with  which  we  shall 
spend  most  of  our  time  in  the  experiments.     If  it  were 
not  for  the  electromagnets,  which  are  made  with  iron 
and  copper,  we  could  not  have  motors  and  dynamos. 


CHAPTER  II 
PERMANENT  MAGNETISM 

TWENTY  EXPERIMENTS  IN  PERMANENT  MAGNETISM  THAT 
BEAR    DIRECTLY    UPON    THE    CONSTRUCTION    AND    EX- 
PLANATION   OF    MOTORS    AND  DYNAMOS. 

7.  Note.     While  most  of  the  twenty  above-mentioned 
experiments  will  be  found  in  Part  I  of  "The  Study  of 
Elementary  Electricity  and  Magnetism  by  Experiment," 
they  are   repeated  herein  because  they  have  a  direct  bear- 
ing upon  motors  and  dynamos.     A  review  of  these  will 
aid  the  student,  and,  if  he  has  never  actually  performed 
experiments  along  this  line  himself,  he  should  not  fail  to 
follow  out  the  suggested  experimental  work. 

EXPERIMENT  1.    To  study  the  horseshoe  magnet. 

8.  Directions.    If  you  remove  the  soft  iron  "armature" 
or  "keeper"  from  the  end  of  the  horseshoe  magnet  and 
then  move  it  about  over  the  whole  magnet,  you  will  find 
that  the  attraction  for  the  armature  is  greatest  at  the 
ends  of  the  magnet.    There  does  not  seem  to  be  any  pull 
upon  the  small  piece  of  iron  at  the  curved  part  of  the 
magnet,  but  this  part  is  silently  doing  its  part  of  the 
work  just  the  same,  as  you  will  find  by  one  of  the  future 
experiments. 

9.  Discussion.    The  ends  of  the  magnet  are  called  its 
"poles,"  and  the  central  part  that  seems  to  have  no  mag- 
netism  is   called   the   "equator."     Electromagnets   have 
poles,  also,  and  the  location  of  these  poles  becomes  quite 
an  important  matter  in  dealing  with  motors  and  dynamos. 


PERMANENT    MAGNETISM  13 

EXPERIMENT  2.  To  see  what  ordinary  things 
are  acted  upon  by  a  magnet. 

10.  Directions.    With  your  horseshoe  magnet,  try  all 
of  the  different  metals  that  you  can  find,  to  see  which  are 
affected  by  the  magnet.    Try  iron,  copper,  tin,  zinc,  lead, 
wood,  glass,  and  any  other  things  you  have  at  hand. 

11.  Discussion.     Most  bodies,   when  placed   near   a 
magnet,  do  not  seem  to  pay  the  slightest  attention  to  the 
magnet,  and  when  removed  from  the  magnet  they  do 
not  seem  to  have  taken  any  magnetism  with  them.     In 
the  case  of  iron  and  steel,  however — and  a  few  other 
things  might  be  mentioned — we  have  substances  that  are 
really  affected  and  which,  in  certain  cases,  take  some- 
thing from  the  magnet.    Steel,  which  is  a  modified  form 
of  iron,  has  the  property  of  holding  quite  a  little  of  the 
magnetism  when  removed  from  the  magnet,  and  it  is 
this  property  that  makes  it  possible  for  the  horseshoe 
magnet  to  hold  its  magnetism  at  all. 

Substances  that  are  attracted  by  a  magnet  are  called 
"magnetic"  substances,  even  if  they  do  not  hold  the  mag- 
netism afterwards ;  but  a  magnetic  body  is  not  necessarily 
a  magnet. 

12.  Magnetism  is  that  queer  something  or  other  that 
magnets  have  and  give  out  freely  to  surrounding  bodies. 
For  the  student  who  is  working  with  motors  and  dyna- 
mos, it  isn't  necessary  to  stop  and  think  about  the  ether- 
whirls  and  other  theoretical  discussions.    This  matter  has 
been  taken  up  in  some  of  the  author's  other  books,  but 
it  does  not  need  to  be  discussed  here. 

When  we  take  up  the  subject  of  "lines  of  force"  and 
the  "magnetic  field,"  we  shall  find  that  the  space  about 
the  magnet  is  filled  with  "magnetic  lines  of  force"  and 
that  objects  placed  in  this  field  are  bathed  with  invisible 
power  of  some  sort  called  magnetism.  Experiment  2 


14  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

proved  that  all  substances  are  not  affected  by  this  queer 
bath,  and  this  is  a  good  thing;  for  we  must  have  some 
inactive  parts  in  the  motors  and  dynamos. 

EXPERIMENT  3.  To  find  through  what  sub- 
stances magnetism  will  act. 

13.  Directions.     If  you  put  a  small  piece  of  iron  wire 
or  a  little  heap  of  iron  filings  upon  a  sheet  of  stiff  paper 
and  then  move  your  horseshoe  magnet  about  immediately 
under  the  paper,  you  will  see  that  the  paper  does  not 
hold  the  magnetism  back. 

If  you  try  thin  pieces  of  wood,  cardboard,  glass,  and 
various  other  things,  you  will  also  see  that  these  are  like- 
wise unable  to  keep  the  magnetism  from  reaching  the 
iron.  Now,  if  you  try  a  sheet  of  tin  in  place  of  the 
paper,  you  will  find  that  the  magnetism  is  not  so  strong 
as  in  the  case  of  the  other  things  and  that,  if  the  tin  be 
thick  enough,  almost  no  magnetism  will  get  through  to 
attract  the  iron. 

14.  Discussion.     We  say  that  paper,  wood  and  the 
other  things  through  which  magnetism  can  act  are  "trans- 
parent to  magnetism,"  for  the  power  of  the  magnet  can 
pass  through  them.     In  the  case  of  the  tin,  which  is 
really  nothing  more  than  sheet  iron  covered  with  tin, 
the  magnetism,  or  most  of  it,  is  held  back.    We  shall  see, 
further  on,  what  becomes  of  the  magnetism  and  why  iron 
acts  like  a  "screen"  to  magnetism. 

The  fact  that  magnetism  can  act  through  cotton  and 
silk  cloth  is  a  very  important  one,  as  the  covering  on  the 
copper  wires  used  on  motors  and  dynamos  is  either  cot- 
ton or  silk. 

15.  Note.     As  it  will  be  impossible  to  give  herein  all 
of  the  elementary  experiments  on  magnetism  in  connec- 
tion with  the  work  on  motors,  the  student  is  referred  to 
any  good  text-book  on  the  subject,  and  if  he  is  not  thor- 


PERMANENT    MAGNETISM  1$ 

oughly  familiar  with  such  experiments,  he  should  take 
up  the  subject  and  get  at  the  bottom  of  it. 

EXPERIMENT  4.     Making  magnets  from  a  mag- 
net. 

16.  Directions.    When  a  piece  of  steel  is  rubbed  prop- 
erly upon  a  horseshoe  magnet,  magnetism  is  given  to 
the  steel,  which  also  becomes  a  magnet.     The  steel  has 
the  power  of  holding  the  magnetism,  and  it  can  even 
pass  some  of  it  along  to  other  pieces  of  steel. 

EXPERIMENT  5.     To  see  what  is  meant  by  the 
north  pole  of  a  magnet. 

17.  Directions.     If  we  rub  a  sewing-needle  upon  one 
of  the  poles  of  a  permanent  magnet,  we  shall  have  a 
small  straight  magnet,  and  this  is  called  a  "bar  magnet.'' 
It  is  an  easy  matter  to  float  this  small  bar  magnet  upon 
a  cork  in  a  dish  of  water  to  see  if  it  will  turn  to  any 
particular  direction.     One  end  of  it  will  always  turn  to 
the  north. 

18.  Discussion.     The  end  of  a  magnet  that  points  to 
the  north  when  it  is  floated  or  otherwise  suspended  is 
called  its  "north  pole,"  and  the  other  end  is  its  "south 
pole."    The  north  pole  is  also  called  the  "north-seeking" 
pole,  and,  as  the  little  magnet  has  the  power  to  point,  we 
say  that  it  has  "pointing-power."    The  "magnetic  needle" 
and  the  "compass"  work  upon  this  principle  and  depend 
upon  a  small  pivoted  bar  magnet  for  their  action.     The 
student  should  be  provided  with  a  small  magnetic  needle 
for  testing  the  poles  of  his  motors  and  dynamos. 

EXPERIMENT  6.     Attractions  and  repulsions  of 
magnets. 

19.  Directions.     After  you  have  made   a   small   bar 
magnet  with  a  needle,  or  you  can  use  your  compass  in- 
stead, you  should  experiment  with  them  to  find  out  the 
laws  of  magnetism.     If  you  try  to  touch  the  north  pole 


l6  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

of  the  horseshoe  magnet,  which  should  be  marked  with 
a  line  or  with  an  N,  to  the  end  of  the  little  floating  bar 
magnet  that  points  to  the  north,  you  will  find  that  they 
actually  repel  each  other.  If  you  try  the  opposite  poles, 
that  is,  a  north  with  a  south,  you  will  find  that  they 
attract  each  other. 

20.  Discussion.  The  attractions  and  repulsions  of 
these  little  magnets  are  strong  enough  to  move  a  freely- 
suspended  magnet,  and  to  show  that  real  motion  can  be 
produced  by  the  action  of  one  magnet  upon  the  other. 
As  will  be  seen  when  we  come  to  the  experiments  upon 
electromagnets,  it  is  this  action  of  attraction  or  repulsion 
that  causes  the  armature  of  the  electric  motor  to  revolve. 

EXPERIMENT  7.  To  see  if  we  can  make  more 
than  two  poles  in  a  bar  magnet. 

21t  Directions.  Place  a  sewing-needle  upon  the  table, 
and  hold  it  down  with  your  finger  while  you  touch  its 
point  with  the  south  pole  of  your  magnet.  Lift  the  mag- 
net straight  from  the  needle,  touch  the  middle  part  with 
the  north  pole,  and,  finally,  the  head  of  the  needle  with 
the  south  pole  again.  Now  if  you  dip  the  needle  into 
iron  filings  you  will  find  that  you  have  made  three  poles, 
for  the  filings  will  stick  to  it  in  three  places. 

You  should  test  these  three  places  with  your  compass 
to  find  out  whether  the  poles  are  north  or  south. 

22.  Discussion.  It  seems  rather  strange  that  we  can 
"have  a  bar  magnet  with  three  or  more  poles,  and  that 
we  can  make  them  north  or  south  as  we  desire,  but  such 
is  the  case,  and  we  can  have  as  many  poles  as  there  are 
places  touched  with  the  magnet. 

Such  poles  are  called  "consequent  poles,"  and  they  are 
made  use  of  in  the  construction  of  motors  and  dynamos. 
They  will  be  studied  again  when  we  take  up  experiments 
with  the  motor. 


PERMANENT    MAGNETISM  If 

EXPERIMENT  8.  To  study  the  theory  of  magnet- 
ism. 

23.  Directions.    If  we  place  a  little  pile  of  iron  filings 
upon  a  piece  of  paper  and  then  draw  a  pencil  or  other 
unmagnetized  thing  lightly  over  it,  we  shall  find  that  the 
pencil  has  made  some  little  furrows  through  the  filings, 
and  there  will  be  nothing  else  that  can  be  seen.    Now,  if, 
in  place  of  the  pencil,  we  draw  one  end  of  a  bar  magnet 
through  the  filings,  we  shall  see  that  something  has  hap- 
pened besides  the  making  of  the  grooves. 

24.  Discussion.     Whenever  a  magnet  acts  by  contact 
upon  the  pile  of  filings,  as  explained  above,  we  find  that 
the  filings  have  been  brought  into  line  and  that  they 
point  in  the  same  direction.     Most  of  the  particles  of 
filings  have  been  made  to  change  their  first  positions  and 
take  up  new  lines.     Each  little  piece  of  iron  has  been 
magnetized,  and,  although  it  could  not  follow  the  magnet 
bodily,  it  has  at  least  turned  upon  a  pivot,  like  the  com- 
pass-needle, to  watch  the  magnet  disappear. 

Every  bar  of  steel  is  composed  of  very  small  particles, 
which  are  called  molecules,  and  it  is  supposed  that  these 
molecules  have  the  power  to  turn  upon  their  axes  when 
the  magnet  is  rubbed  over  the  steel.  Of  course  they  are 
too  small  to  be  seen,  but  the  experiment  with  the  filings 
should  aid  in  understanding  how  they  act  under  the  in- 
fluence of  the  magnet.  In  this  case,  the  pile  of  filings 
takes  the  place  of  the  piece  of  steel,  while  each  piece  of 
filing  takes  the  place  of  a  molecule.  There  are  experi- 
ments that  show  that  the  pile  of  filings  becomes  mag- 
netized and  gets  poles  like  any  piece  of  iron. 

When  as  many  as  possible  of  the  particles  of  a  piece 
of  steel  have  been  brought  into  line,  we  say  that  the 
steel  has  been  "saturated"  with  magnetism.  We  shall 
see,  later,  that  we  can  magnetize  a  piece  of  steel  by  using 


l8  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

the  electric  current  instead  of  a  permanent  magnet.  Each 
little  molecule  of  the  steel  is  supposed  to  be  a  very  small 
magnet,  even  before  we  try  to  bring  it  into  line,  so  that 
all  that  is  really  necessary  is  to  have  the  magnet  or  the 
electricity  swing  the  molecules  around  so  that  they  will 
all  point  in  the  same  direction. 

EXPERIMENT  9.  To  find  whether  soft  iron  will 
permanently  retain  magnetism. 

25.  Directions.    Rub  a  short  length  of  soft  annealed 
iron  wire  upon  your  horseshoe  magnet  to  magnetize  it  as 
you  did  the  needle,  and  then  test  it  by  seeing  how  many 
iron  filings  it  will  lift.    Try  a  needle  again  and  compare 
the  strength  of  this  with  that  of  the  wire. 

26.  Discussion.     We  find  that,  although  the  soft  iron 
wire  is  strongly  attracted  by  the  magnet,  it  does  not  carry 
away  much  magnetism  when  removed  from  the  magnet. 
In  the  case  of  the  steel,  however,  we  find  that  this  holds 
the  magnetism  very  well,  and  that  it  will  lift  quite  a  load 
of  the  filings. 

This  power  to  retain  the  magnetism  is  called  "reten- 
tivity,"  or  "coercive  force."  From  this  we  see  the  differ- 
ence between  iron  and  steel  at  once,  and  can  understand 
how  one  might  be  better  than  the  other  for  certain  elec- 
trical purposes.  The  fact  that  soft  iron  loses  most  of 
its  magnetism  as  soon  as  it  is  removed  from  the  action 
of  a  magnet  makes  it  suitable  for  many  electrical  ma- 
chines in  which  it  is  absolutely  necessary  to  have  it  act 
in  this  way. 

EXPERIMENT  10.     Hard  steel  and  soft  steel. 

27.  Directions.     Take  a  needle  that  has  been  thor- 
oughly  magnetized,   test   its   lifting-power   with   filings, 
then  place  it  upon  a  piece  of  iron  and  hammer  it  several 
times  to  jar  its  molecules  out  of  line.     Testing  it  again, 
you  will  find  that  it  has  very  little  magnetism. 


PERMANENT    MAGNETISM  19 

Now  take  an  ordinary  wire  nail,  which  is  made  of  what 
is  called  soft  steel,  try  the  same  thing  with  this  and  you 
will  find  that  you  can  hammer  out  part  of  the  magnetism ; 
that  is,  its  retentivity  is  less  than  that  of  steel.  Again, 
try  the  same  thing  with  a  piece  of  soft  iron  wire  and 
you  will  find  that  the  wire  has  almost  no  retentivity. 

28.  Discussion.    It  should  now  be  clear  that,  when  we 
want  to  make  a  permanent  magnet,  we  should  use  good 
hard  steel  that  has  the  proper  retentivity,  and  that,  for 
places  where  we  do  not  want  magnetism  to  last,  we  should 
use  the  softest  of  iron.     There  are  times  where  it  is 
necessary  to  use  soft  steel  or  cast  iron  in  order  to  get 
a  medium  retentivity.     The  choice  of  iron  for  making 
motors-  and  dynamos  depends  largely  upon  the  amount 
of  "carbon"  in  it,  as  it  is  this  element — when  combined 
with   the   iron — which   determines   the   hardness   of  the 
steel. 

EXPERIMENT  11.    About  residual  magnetism. 

29.  Directions.     When  we  magnetized  the  soft  iron 
wire  and  then  pounded  it  with  a  hammer,  we  found  that 
it  lost  all  of  its  magnetism,  or  practically  all  of  it.     Now 
try  again,  and,  before  you  strike  it  with  the  hammer,  see 
if  the  magnetized  wire  will  lift  a  few  iron  filings;  that 
is,  does  it  really  hold  some  of  the  magnetism  after  it  has 
been  taken  from  the  magnet? 

30.  Discussion.     Even  soft  iron  will  show  some  indi- 
cations of  magnetism  when  it  is  first  taken  from  the  mag- 
net, and,  even  if  it  does  lose  the  greater  part  of  it  when 
pounded,  there  is  a  slight  tendency  towards  retentivity. 
This  magnetism  that  iron  holds  is  called  "residual  mag- 
netism," and  it  is  this  magnetism  that  is  made  use  of  in 
the  dynamo  to  start  the  production  of  electricity,  as  will 
be  explained  later.     The  principal  thing  for  the  student 
to  remember  now  is  that  it  is  important,  in  the  case  of 


20  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

dynamos,  for  some  magnetism  to  remain  in  the  iron  after 
the  dynamo  has  been  stopped.  This  is  certainly  one  prac- 
tical use  of  residual  magnetism. 

EXPERIMENT  12.    About  induced  magnetism. 

31.  Directions.    Place  an  unmagnetized  sewing-needle 
upon  a  piece  of  stiff  paper,  then  move  your  horseshoe 
magnet  around  under  the  paper.     Test  the  needle  for 
magnetism  by  seeing  if  it  will  lift  any  filings. 

32.  Discussion.     We   learned   in   Experiment  3   that 
magnetism  will  pass  through  paper,  and  so  we  expected 
that  the  needle  would  move  around  by  the  pulling-effect 
of  the  magnet.    As  the  steel  of  the  needle  has  consider- 
able retentivity,  it  held  the  magnetism  very  well  and  was 
strong  enough  to  lift  almost  as  many  filings  as  it  did 
when  it  was  magnetized  directly  upon  the  magnet. 

We  see  from  this  that  we  can  magnetize  steel  without 
even  touching  it  directly  with  a  magnet.  This  needle 
is  said  to  have  been  "magnetized  by  induction" ;  that  is, 
it  was  magnetized  at  a  distance,  without  actual  contact. 
This  effect  is  brought  into  play  in  every  electromagnet 
when  it  is  energized  by  the  electric  current  flowing 
through  the  coil  of  wire.  If  magnetism  did  not  act 
through  the  air  and  at  a  distance,  many  of  the  effects 
that  we  now  get  would  be  impossible.  Induction-coils, 
dynamos,  motors,  telegraph  instruments  and  numberless 
other  electrical  machines  depend  upon  this  simple  thing 
for  their  action  and  usefulness. 

EXPERIMENT  13.  About  polarization  and  pole- 
pieces. 

33.  Directions.    If  you  place  a  soft  iron  wire  about  an 
inch  long  upon  one  pole  of  your  horseshoe  magnet  so 
that  it  will  point  away  from  the  magnet,  you  will  find 
that  the  end  of  the  wire  will  lift  filings,  also.    With  your 
swinging  needle  test  the  end  of  the  wire  for  poles,  when 


PERMANENT    MAGNETISM  21 

placed  upon  the  north  and  then  upon  the  south  pole  of 
the  magnet.  Try  the  same  thing  with  a  piece  of  paper 
between  the  magnet  and  the  wire,  to  see  if  you  can  lift 
filings. 

34.  Discussion.     A  piece  of  iron,  when  placed  upon 
the  pole  of  a  magnet,  becomes  magnetized  by  induction, 
even  if  it  does  not  touch  the  magnet  at  the  end.  The  effect 
is  the  same  as  for  the  needle,  when  it  was  magnetized 
through  the  paper,  and,  as  the  wire  could  lift  iron,  we 
know  that  it  had  poles  at  the  end.     By  means  of  the 
compass-needle  we  find  that  the  pole  at  the  lower  end  of 
the  wire  is  the  same  as  that  of  the  magnet  to  which  it 
is  attached;  that  is,  if  the  wire  hangs  upon  the  north 
pole  of  the  magnet,  the  lower  end  of  the  wire  will  also 
be  a  north  pole. 

This  wire  is  said  to  have  been  "polarized,"  and  the 
pieces  of  iron  which  take  up  these  poles  by  being  in 
contact  with  a  magnet  are  called  "pole-pieces."  As  will 
be  seen  when  we  look  more  thoroughly  into  the  construc- 
tion of  motors  and  dynamos,  pole-pieces  are  used  on 
most  every  machine  of  this  kind  to  lead  the  lines  of  force 
where  they  are  most  needed. 

EXPERIMENT  14.  To  study  combinations  of  pole- 
pieces. 

35.  Directions.     If  you  put  two  short  lengths  of  soft 
iron  wire  upon  the  same  pole  of  a  magnet,  as  suggested 
in  Fig.  i,  you  will  find  that  both  of  the  lower  ends  of  the 
wires  will  lift  filings  and  that  they  are  of  the  same  polar- 
ity.    This  will  be  evident,  as  they  will  repel  each  other 
if  they  are  near  enough  to  act. 

If  you  now  hammer  the  wires  a  little  to  remove  the 
residual  magnetism  and  then  place  them  upon  the  op- 
posite poles,  as  in  Fig.  2,  they  will  still  be  able  to  lift 
filings,  but  they  will  attract  each  other  when  near  enough. 


22  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

This  might  be  expected   from  the  information  derived 
from  Experiment  13. 

36.  Discussion.  From  the  latter  part  of  this  experi- 
ment we  see  that  the  two  movable  poles  tend  to  rush  to- 
ward each  other,  and  that  there  must  be  a  pull  upon  the 
poles  of  the  regular  horseshoe  magnet  in  their  attempt 
to  get  nearer  each  other  to  shorten  the  distance  the  lines 
of  force  have  to  travel  in  getting  from  one  pole  to  the 
other.  This  shows  the  necessity  of  having  rigid  pole- 
pieces  on  motors  and  dynamos  so  that  they  will  keep 
the  proper  distance  apart. 


Fig.  2 

EXPERIMENT  15.  To  study  the  effect  of  a  con- 
tinuous pole-piece. 

37.  Directions.     In  place  of  the  two  wires  used   in 
Experiment  14,  bend  one  piece  as  shown  in  Fig.  3,  place 
the  two  ends  upon  the  poles  of  the  magnet,  then  test  the 
curved  part  for  magnetism  to  see  if  it  will  lift  any  filings. 

38.  Discussion.     In  this  continuous  pole-piece  there 
was  no  tendency  to  lift  iron,  showing  that  there  was  no 
pole  at  the  bend  of  the  wire.     If  we  consider  the  wire  a 
small  horseshoe  magnet  that  is  magnetized  by  induction, 
we  can  understand  that  its  poles  are  at  the  ends  and 
that  it  has  no  power  to  attract  near  its  equator.    (Exp.  i.) 

If  the  wire  be  bent  a  little  more,  as  in  Fig.  4,  a  conse- 
quent pole  will  be  made  at  the  bend  and  we  shall  be 
able  to  lift  small  pieces  of  iron,  as  indicated. 


PERMANENT    MAGNETISM  23 

In  the  case  of  motors  and  dynamos  with  two  poles,  we 
want  the  lines  of  force  to  pass  in  great  quantities  be- 
tween the  poles  or  pole-pieces,  so  we  do  not  want  the 
pole-pieces  to  touch  each  other.  We  shall  see  that  the 
lines  of  force  on  their  way  from  one  pole  to  the  other 
pass  through  certain  coils  of  wire,  and  that  this  is  neces- 
sary to  produce  motion  in  the  motor  or  electricity  in  the 
dynamo.  Whenever  the  poles  are  joined  by  a  metal  strip, 
as  in  the  case  of  many  small  motors,  this  strip  is  made 
of  brass  and  not  of  iron;  for  iron  would  sidetrack  some 
of  the  lines  of  force,  as  did  the  bent  wire  of  Fig.  3. 


Fig.  3  Fig.  4 

EXPERIMENT  16.  To  study  the  magnetic  field  of 
the  horseshoe  magnet. 

39.  Directions.     Remove  the  armature  of  the  horse- 
shoe magnet,  place  the  magnet  upon  a  table,  put  a  piece 
of  stiff  paper  over  it,  then  sprinkle  some  fine  iron  filings 
upon  the  paper.    Tap  the  paper  gently  to  assist  the  par- 
ticles of  filings  as  they  try  to  swing  around. 

40.  Discussion.     If  you  have  the  proper  filings,  you 
will  see  that  they  arrange  themselves  in  lines  and  curves 
about  the  poles  of  the  magnet,  and  that  they  indicate 
roughly  how  far  out  the  force  of  the  magnet  reaches. 

If  you  place  your  compass-needle  in  various  positions 
about  the  magnet,  you  will  find  that  this  is  more  delicate 
than  the  filings  and  that  the  "magnetic  field"  reaches  out 
into  space  on  all  sides  of  the  magnet.  The  picture  made 
by  the  filings  is  called  a  "magnetic  figure,"  and  we  shall 


24  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

use  these  to  study  the  magnetic  fields  of  the  motors  de- 
scribed in  this  book. 

We  see  from  this  experiment  that  the  little  particles  of 
filings  become  magnets,  by  induction,  and  that,  when  they 
are  assisted  by  the  tapping,  they  get  into  the  same  lines 
as  those  taken  by  the  compass-needle  when  it  is  moved 
about  in  the  field.  The  magnetism  travels  from  one  pole 
to  the  other  in  curved  lines,  and,  for  convenience,  we 
agree  that  they  start  from  the  north  pole  of  the  magnet 
and  pass  through  the  air  to  the  south  pole.  They  seem 
strongest  near  the  poles,  and  from  the  magnetic  figures 
we  see  that  there  is  quite  a  space  about  the  ends  of  the 
magnet  from  which  these  lines  pour  in  their  wild  rush 
to  get  to  the  south  pole. 

EXPERIMENT  17.  Magnetic  field  with  armature 
in  place. 

41.  Directions.     Lay  the  horseshoe  magnet  upon  the 
table  as  before,  but  with  its  soft-iron  armature  in  place 
upon  the  poles,  then  make  its  magnetic  figure  with  the 
filings.    Study  the  space  near  the  poles  and  armature  and 
note  whether  the  lines  of  force  are  as  strong  as  when 
the  armature  was  removed. 

42.  Discussion.    From  this  it  is  evident  that  the  lines 
of  force  go  through  the  iron  armature  instead  of  passing 
out  through  the  air.    Of  course,  many  of  them  leak  out 
of  the  sides  of  the  poles  and  get  past  the  armature ;  but 
the  greater  part  of  them  take  the  easy   path  through 
iron  instead  of  the  path  through  the  air,  which  offers  a 
high  resistance. 

There  were  no  well-marked  curves  directly  over  the 
armature,  and  this  indicates  that  at  this  point  the  lines 
of  force  do  not  leak  out  into  the  air ;  on  the  contrary,  they 
are  only  too  glad  to  hide  themselves  in  the  iron  as  they 
swiftly  pass  around  and  around  the  circuit. 


PERMANENT    MAGNETISM  25. 

This  experiment  should  now  make  it  clear  why  there 
was  no  pull  upon  the  armature  when  it  was  placed  at 
the  equator  of  the  horseshoe  magnet  in  Experiment  I. 
We  do  not  get  poles  and  a  pulling-effect  unless  the  lines 
of  force  come  out  into  the  air  on  their  way  from  the 
north  pole  to  the  south  pole.  Wherever  there  is  a  leak- 
age of  lines  of  force  we  have  poles. 

EXPERIMENT  18.    Lines  of  force  and  air-gaps. 

43.  Directions.     Lay  the  horseshoe  magnet  upon  the 
table,  as  before,  place  a  couple  of  matches  against  its 
poles,  and  then  put  the  armature  so  that  it  will  press 
against  the  matches  while  trying  to  get  to  the  poles. 
Make  the  magnetic  figure  of  this  arrangement  and  note 
especially  what  the  filings  do  over  the  spaces  occupied  by 
the  matches. 

44.  Discussion.     Magnetic  lines  of  force  will  go  out 
of  their  way  to  get  to  a  piece  of  iron  on  their  way  around 
the  circuit  between  the  poles  if  the  distance  to  travel  in 
the  air  is  thus  shortened.    If  we  want  to  carry  the  mag- 
netism across  any  space  without  losing  very  much  in 
power,  we  can  fill  the  space  with  soft  iron,  and  if  air- 
gaps  have  to  be  left,  as  in  the  case  of  the  armatures  of 
motors  and  dynamos,  the  air-gaps  are  made  as  small  as 
practicable,  thus  making  the  resistance  to  the  lines  of  force 
as  small  as  possible. 

EXPERIMENT  19.     Hollow  armatures. 

45.  Directions.     Place  the  horseshoe  magnet  upon  the 
table  again,  but  this  time  lay  an  iron  ring  against  the 
poles,  as  in  Fig.  5.    An  ordinary  iron  washer  will  do  for 
this  experiment.     Sprinkle  iron  filings  upon  the  paper 
placed  over  this  arrangement  and  note  especially  how  the 
lines  of  force  act  over  the  hole  in  the  ring.     Do  they 
seem  prominent,  or  are  they  few  and  indistinct? 

46.  Discussion.    The  iron  ring  in  this  experiment  acts 


26  STUDY  OF  ELECTRIC  MOTORS  BY  EXPERIMENT 

very  much  like  the  regular  armature,  inasmuch  as  it 
seems  to  take  most  of  the  lines  of  force  and  to  make  an 
easy  path  for  them.  The  field  seems  to  be  particularly 
weak  over  the  hole  in  the  ring,  and  this  indicates  that 
the  lines  of  force  bend  around  the  hole  to  follow  the 
iron,  and  so  they  do  not  leak  out  into  the  air  to  attract 
the  filings. 

We  have,  here,  the  same  thing  on  a  small  scale  as  in 
the  round  armatures  of  dynamos  and  motors,  which  are 


Fig.  5  Fig.  6 

also  made  hollow.  In  large  machines  it  is  important  to 
have  the  rapidly  revolving  armatures  hollow  to  give  them 
the  required  ventilation  and  to  allow  the  proper  wiring. 
Besides,  on  large  machines,  a  solid  armature  would  be 
too  heavy. 

EXPERIMENT  20.  To  study  a  certain  combina- 
tion of  two  magnets. 

47.  Directions.     Place  two  horseshoe  magnets  upon 
the  table  with  their  like  poles  together,  as  indicated  in 
Fig.  6,  then  make  the  magnetic  figure  of  the  combination 
as  described  before. 

Note  especially  whether  the  lines  of  force  pass  across 
the  space  between  the  poles  or  whether  the  field  seems 
weak  there. 

48.  Discussion.    It  might  seem  to  the  student  that  the 
lines  of  force  should  pass  around  through  the  curved 
parts  of  the  magnets  and  not  rush  across  the  air-space  at 
the  middle  of  the  combination.     But  if  you  consider  the 
fact  that  these  lines  are  streaming  out  of  both  north 


PERMANENT    MAGNETISM  2/ 

poles  in  their  endeavor  to  get  to  the  south  poles,  you 
can  see  why  they  are  only  too  willing  to  rush  across  the 
short  air-gap  to  the  desired  pole. 

Many  of  the  larger  motors  and  dynamos  are  somewhat 
similar  in  construction  to  the  plan  given  in  these  two 
magnets.  Diagrams  will  be  given  later  to  show  the 
route  of  the  lines  of  force  in  such  combinations. 


CHAPTER  III 
EXPERIMENTAL  APPARATUS 

EXPLAINING  APPARATUS   USED   IN    CONNECTION   WITH 
MOTOR  AND  DYNAMO  EXPERIMENTS. 

49.  Experimental  Apparatus.  While  it  is  taken  for 
granted  that  the  student  is  familiar  with  all  of  the  simple 
apparatus  that  is  required  for  doing  experiments  with 
motors  and  dynamos,  a  short  discussion  of  them  will  be 
given  herein,  however,  as  some  of  the  pieces  used  by 
the  author  are  of  special  design.  In  case  the  reader 
wishes  to  make  his  own  apparatus  for  these  and  other 
experiments,  he  is  referred  to  the  author's  book  on  "Elec- 
trical Handicraft."  All  of  the  apparatus  needed  for  the 
experiments  can  be  purchased  in  case  the  student  does 


not  wish  to  make  it.  (See  list  at  the  back  of  this  book.) 
Do  not  get  the  idea  from  the  numerous  pieces  described 
that  all  of  them  are  needed.  A  variety  is  given  so  that 
the  student  can  more  easily  find  out  what  he  wants  for 
his  special  work. 

50.  Strap  Key,  Style  A.  Fig.  7  illustrates  the  use  of 
a  simple  strap  key,  a  dry  battery  being  shown  at  the 

28 


EXPERIMENTAL  APPARATUS 


29 


right  and  an  electromagnet  at  the  left.  When  the  finger- 
piece  of  the  key  is  depressed,  the  current  can  flow,  be- 
cause two  of  the  metal  parts  are  forced  together,  and,  as 


Fig.  8 


soon  as  the  pressure  is  removed,  the  spring  of  the  strap 
separates  the  two  parts  and  the  circuit  is  broken  again. 

Fig.  8  is  a  top  view  of  a  very  handy  strap  key,  which 
is  made  of  nickel-plated  brass  straps,  with  black  finger- 


Q 


Fig.  9 

piece,  all  being  mounted  upon  a  narrow,  bright  red  base. 
The  holes  at  the  right  and  left  are  eyelet  holes,  the  eyelets 
also  being  nickel-plated.  The  whole  is  to  be  screwed  to 
the  table  or  to  the  wall  by  wood  screws  that  are  to  pass 


30  STUDY  OF  ELECTRIC  MOTORS  BY  EXPERIMENT 

through  the  two  holes,  the  wires  from  the  battery  or 
small  dynamo  being  fastened  under  the  heads  of  the 
screws.  The  screw-head  shown  at  the  center  is  the  head 
of  the  adjusting-screw,  which  is  used  to  adjust  the 
height  of  the  brass  key-strap  above  the  lower  contact. 
51.  Strap  Key,  Style  B.  Fig.  9  shows  a  different  form 


Fig.  10 

of  key  (Apparatus  No.  84  in  "Electrical  Handicraft") 
made  with  nickel-plated  brass  straps,  black  finger-piece, 
and  spring  binding-posts,  all  mounted  upon  a  black  base 
having  red  cleats  at  the  bottom  and  nickel-plated  corner 
nails.  The  current  enters  the  key  at  I  and  leaves  at  O, 
when  the  key-strap  is  depressed.  This  has  no  side  switch. 
52.  Strap  Key,  with  Side  Switch.  In  some  experi- 
ments you  want  to  send  intermittent  currents,  and  then, 
perhaps,  you  would  like  to  have  the  current  flow  for 
some  time  without  holding  the  key  down.  Fig.  10  shows 
a  form  of  key  with  which  this  can  be  done.  Wire  SW 
connects  the  underside  of  the  nickel-plated  screw  binding- 


EXPERIMENTAL  APPARATUS  3! 

post,  I,  with  the  underside  of  the  pivot  of  the  small 
switch-arm.  Now,  when  the  switch  is  turned  so  as  to 
rest  upon  the  contact-point,  CP,  current  will  pass  out 
through  O,  even  if  the  key  does  not  touch  the  lower 
strap.  This  is  the  sort  of  key  that  is  used  in  telegraph 
work,  and  it  is  a  very  handy  form  for  many  experiments. 
53.  Double-Key  Current-Reverser.  In  Fig.  n  we 
have  the  top  view  of  a  current-reverser  (Apparatus 


Fig.  ii 

No.  128  in  "Electrical  Handicraft"),  which  is  suggested 
here  as  it  is  very  useful  in  motor  experiments,  and  be- 
cause it  is  so  constructed  that  it  can  be  used  in  many 
ways.  This  reverser  is  made  of  nickel-plated  brass  straps, 
nickel-plated  screw  binding-posts,  and  black  finger-pieces, 
all  being  mounted  upon  a  dead-black  base  with  bright 
red  cleats.  Both  of  the  key-straps  press  up  against  the 
upper  strap  unless  depressed  to  touch  the  lower  strap 
marked  I.  This  little  reverser  is  so  made  that  it  can 
be  used  also  for  a  key,  push-button,  and  two-point  switch. 
It  really  consists  of  two  or  three  pieces  of  apparatus,  and 
is  extremely  handy. 


.32 


STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 


54.  How  this  reverser  works.  Fig.  12  shows  how 
this  piece  of  apparatus  can  be  used  to  reverse  the  direc- 
tion of  the  current  in  an  electromagnet  or  other  coil  of 
wire.  A  dry  cell  is  shown  at  the  right  of  the  figure,  with 
wires  leading  from  it  to  the  two  binding-posts  C  and  Z 
of  the  reverser,  C  standing  for  the  carbon  and  Z  for  the 
zinc  of  the  cell.  When  the  current  comes  from  the  car- 
bon of  the  cell,  it  can  go  no  farther  than  Strap  I,  be- 
cause the  other  straps  are  above  it. 


Fig.  12 

If  Key  2  be  pressed  far  enough  to  strike  the  lower 
strap,  the  current  will  pass  along  Key  2,  which  does  not 
now  touch  4,  and  out  through  X  to  the  coil  and  back  to 
the  reverser  at  Y.  It  will  then  pass  from  3  to  4,  and 
then  back  to  the  cell. 

When  Key  3  is  pressed,  the  current,  which  still  enters 
the  reverser  at  C,  will  pass  to  3  and  out  at  Y.  It  is 
evident,  then,  that  by  this  simple  arrangement  the  cur- 
rent can  be  made  to  pass  through  the  coil  in  either  di- 
rection by  pressing  the  proper  key. 

We  shall  see  that  with  the  aid  of  this  reverser  and 
with  motors  of  the  proper  design,  we  can  reverse  motors 
and  do  various  interesting  experiments. 

55.  Two-Point  Switch.  Fig.  13  shows  the  full-size 
top  view  of  a  two-point  switch  (Apparatus  No.  62  in 
"Electrical  Handicraft")  that  can  be  used  to  advantage 
in  some  of  the  motor  experiments.  The  five  holes  show 
the  location  of  the  nickel-plated  eyelets,  the  switch-arm 


EXPERIMENTAL  APPARATUS 


33 


being  at  the  middle.  Dotted  lines  WA  and  WB  repre- 
sent wires  under  the  bright-red  base,  and  these  connect 
the  two  eyelets  at  the  ends  with  those  upon  which  the 
switch-arm  is  turned.  Connections  are  made  by  means 
of  screws  put  into  the  two  end  eyelets  and  the  middle 


Fig.  13 

one,  the  wires  being  held  under  the  screw-heads  when 
the  switch  is  screwed  to  the  table. 

Fig.  14  shows  one  use  for  this  switch,  in  which  the 
current  from  a  dry  cell  may  be  turned  to  either  of  two 
things  as,  for  example,  a  bell  or  motor.  This  may  also 
be  used  to  switch  the  current  from  a  small  dynamo,  the 
battery  being  replaced  by  the  dynamo.  In  either  case,  the 


Fig.  14 


current  enters  the  switch  at  Q,  from  which  it  will  pass 
to  the  desired  instrument  by  turning  the  switch-arm  to 
the  proper  contact-point. 

56.  Rheostats  are  adjustable  resistances  that  are  so 
arranged  that  different  lengths  of  resistance-wire  can  be 
thrown  into  the  circuit  by  merely  turning  a  switch-arm 
to  the  desired  point.  Numerous  kinds  of  rheostats  are 


34 


STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 


made,  but  the  ones  herein  described  have  been  designed 
for  students'  use.  With  these  rheostats  we  can  regulate 
the  speed  of  motors,  vary  the  brilliancy  of  the  electric 
lamps  and  do  a  number  of  things.  Some  of  the  small 
rheostats  are  so  made  that  they  so  gradually  increase  or 
decrease  the  speed  of  a  motor  that  there  are  no  distinct 
changes  or  jumps.  It  is  much  more  interesting  to  have 
the  motor  leap  ahead  a  little  as  each  contact-point  is 


i  i  \ 


1*2- 


Fig.  15 

reached  than  to  have  no  such  changes,  and  it  is  more  fun 
to  have  the  motor  sing  a  different  tune  as  each  distinct 
speed  is  reached.  This  is  the  plan  used  on  trolley-cars 
and  in  other  commercial  power-plants,  and  that  is  why 
this  sort  of  rheostat  is  used  in  these  experiments. 

57.  Five- Point  Rheostat.  Fig.  15  shows  the  top  of 
a  neat  and  useful  five-point  rheostat,  the  resistance-wires 
under  the  base  being  shown  by  dotted  lines  (Apparatus 
No.  124  in  "Electrical  Handicraft").  This  instrument 
can  be  placed  in  the  battery  or  small  dynamo  circuit  by 


EXPERIMENTAL  APPARATUS 


35 


joining  the  wires  to  the  nickel-plated  screw  binding- 
posts  X  and  Y.  If  the  current  enters  at  X  when  the 
switch-arm  is  in  the  position  shown  in  the  figure,  it  will 
be  obliged  to  pass  through  the  entire  length  of  the  re- 


Fig.  16 

sistance-wire  and  out  through  wire  W  before  it  can  leave 
the  instrument  by  way  of  binding-post  Y. 

If  we  now  move  K  to  the  second  nickel-plated  contact- 
point  2,  two  parts  of  the  resistance-wire  will  be  cut  out 
of  the  circuit,  thus  reducing  the  resistance.  By  moving 
K  to  contact-point  3,  about  one-half  of  the  resistance  will 
have  been  cut  out,  and  when  K  rests  upon  contact-point 
5,  the  current  will  pass  from  X  to  Y  with  almost  no  re- 


36  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

sistance.  This  is  the  general  action  of  most  rheostats, 
and  we  shall  see  how  the  two  kinds  described  herein  can 
be  used  in  the  experiments.  They  are  mounted  upon 
dead-black  bases  and  have  a  fine  appearance.  The  five- 
point  rheostat  is  designed  to  regulate  the  current  from 
two  dry  cells  when  they  are  used  to  run  small  motors,  as, 
for  example,  the  "St.  J.  Motor  No.  i."  When  current 
is  derived  from  small  dynamos,  the  "Eleven-point  Rheo- 
stat" should  be  used. 

58.  Eleven-Point  Rheostat.  Fig.  16.  Although  this 
rheostat  is  built  in  a  way  that  is  a  little  different  from 
that  used  for  the  five-point  rheostat  just  described,  the 
general  principle  of  the  two  is  the  same  (Apparatus 


Fig.  17 

No.  125  in  "Electrical  Handicraft").  The  resistance  of 
this  instrument  is  quite  a  little  more  than  that  of  the 
•other,  as  it  has  been  designed  to  work  with  three  dry 
cells  in  connection  with  small  motors  and  for  experi- 
mental work  with  miniature  incandescent  lamps.  In  con- 
nection with  small  lighting-plants  run  on  the  current 
from  small  dynamos,  this  rheostat  can  be  used  to  regu- 
late the  brilliancy  of  the  lamps,  and  it  is  also  useful  in 
protecting  lamps  and  other  apparatus  from  too  much 
current. 

This  instrument  looks  very  well  when  mounted  upon 
a  switchboard,  as  the  contact-points  and  other  parts  are 
nickel-plated. 

59.  Current  Detectors.     We  shall  see  by  the  experi- 


EXPERIMENTAL  APPARATUS  37 

ments  upon  this  subject  that  an  ordinary  coil  of  wire 
acts  like  a  magnet  when  a  current  of  electricity  passes 
through  it,  and  that  the  electromagnetism  produced  by 
the  coil  acts  upon  the  pivoted  needle-magnet  and  causes 
it  to  move.  We  really  have  two  magnets  acting  upon 
each  other,  when  the  current  is  turned  on.  Uses  for 
these  detectors  will  be  given  under  the  proper  experi- 
ments. 

60.  Simple  Current  Detector.  Fig.  17  shows  a  form 
of  current  detector  that  will  do  for  many  experiments, 
and  it  is  very  inexpensive.  The  coil  is  mounted  upon  a 


Fig.  18 

narrow  base,  the  ends  of  the  wire  being  fastened  to  eye- 
lets which  also  act  as  binding-posts.  Screws  are  used  to 
fasten  the  detector  to  the  table,  the  circuit-wires  being 
held  under  the  heads  of  the  screws.  The  needle  is  made 
of  narrow  spring  steel  and  is  pivoted  at  the  center,  as 
shown. 

61.  Handy  Current  Detector.  Fig.  18  shows  a  handy 
form  of  detector  that  has  the  coil  and  nickel-plated  spring 
binding- posts  mounted  upon  a  black  base  (Apparatus 
No.  22  in  "Electrical  Handicraft").  This  can  be  set  any- 
where, as  it  does  not  have  to  be  screwed  to  the  table. 
(For  the  construction  of  galvanoscopes  and  delicate  de- 
tectors see  Chap.  3  in  "Electrical  Handicraft.") 


CHAPTER  IV 
ELECTROMAGNETISM 

TEN    EXPERIMENTS   ON    ELECTROMAGNETISM    THAT    AID   IN 

UNDERSTANDING  THE  CONSTRUCTION  AND  OPERATION 

OF   MOTORS  AND  DYNAMOS. 

62.  Electromagnetism  is  the  name  given  to  magnetism 
that  is  produced  by  electricity.  In  Experiment  16,  we 
saw  that  a  magnetic  needle  was  affected,  when  placed  in 
the  field  of  a  permanent  magnet,  and  that  its  north  pole 
always  pointed  in  the  direction  in  which  the  lines  of 
force  pass  on  their  way  from  the  north  to  the  south  pole 
of  the  magnet.  We  must  now  try  some  experiments  that 
will  show  how  magnetism  and  electricity  work  together 
in  motors  and  dynamos. 


EXPERIMENT  21.  Electric  current  and  magnetic 
needle. 

63.  Directions.  If  you  make  up  a  circuit  similar  to 
that  shown  in  Fig.  19  consisting  of  a  battery  DC,  a  key, 
and  one  of  the  current  detectors  OC,  just  described,  you 
will  find  that  the  needle  of  the  detector  will  swing  rap- 
idly each  time  you  close  the  circuit  at  the  key,  and  that 
it  will  go  back  to  its  original  position  as  soon  as  you 

38 


ELECTROMAGNETISM  39 

open  the  circuit  again.  The  needle,  of  course,  should  be 
directly  under  the  coil  when  it  is  at  rest;  that  is,  the  coil 
should  be  placed  in  a  north  and  south  line. 

64.  Discussion.  From  this  we  see  that  the  coil  of  the 
detector  becomes  a  small  electromagnet  the  instant  the 
current  passes  through  it  and  that,  best  of  all,  it  loses  its 
magnetism  as  soon  as  the  circuit  is  opened.  We  have 
here  the  two  magnetic  fields  acting  upon  each  other  like 
the  two  fields  of  two  permanent  magnets. 


Fig.  20 

EXPERIMENT  22.     Reversing  the  current  in  the 
detector. 

65.  Directions.     If  we  now  put  a  current-reverser  in 
the  circuit  in  place  of  the  key,  as  suggested  in  Fig.  20, 
we  shall  find  that  the  needle  will  turn  in  a  direction  de- 
pending upon  the  particular  lever  that  is  pressed. 

66.  Discussion.    We  have,  then,  in  this  simple  coil  of 
wire  on  the  detector,  a  plan  by  which  we  can  tell  the 
direction  of  the  current.     If  the  current  passes  through 
the  coil  in  one  direction,  magnetism  is  built  up  in  it  in 
just  the  opposite  way  from  that  in  which  it  is  built  when 
the  current  flows  in  the  opposite  direction. 

EXPERIMENT  23.     Magnetism  from  hollow  coils 
of  wire. 

67.  Directions.     Fig.  21.     If  you  arrange  a  battery, 
reverser,  and  a  hollow  coil  of  wire  as  shown,  you  will 
be.  able  to  reverse  the  current  in  the  coil  at  will,  and 
if  this  coil  be  placed  in  an  east  and  west  line,  with 
your  compass-needle  a  short  distance  away,  you  can 


4O  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

study  the  change  of  magnetism  in  the  coil  as  it  re- 
verses. See  how  far  from  the  coil  the  needle  will  be 
affected. 

68.  Discussion.  Here  we  have  merely  a  coil  of  cop- 
per wire  without  any  iron,  and  still  we  get  poles  with 
attractions  and  repulsions  for  the  compass-needle  every 
time  the  current  passes.  It  is  this  property  that  coils  of 
wire  have  that  makes  them  so  valuable  in  all  electrical 
apparatus. 


" 


"•r 

Fig.  22 


Fig.  21 

EXPERIMENT  24.    About  coils  of  wire  with  cores. 

69.  Directions.    Slip  an  iron  core  through  the  hollow 
coil  used  in  the  last  experiment  and  see  whether  the 
action  upon  the  compass-needle  is  more  or  less  than  be- 
fore. 

70.  Discussion.    When  we  place  an  iron  core  through 
a  coil  of  wire,  we  get  what  is  commonly  called  an  electro- 
magnet, and  we  find  that  the  core  adds  greatly  to  the 
strength  of  the  magnet. 

We  have  already  seen  that  air  does  not  readily  conduct 
the  lines  of  force,  and  so  we  may  expect  that  when  the 
lines  of  force  have  to  push  their  way  through  long  air- 
spaces, the  strength  of  the  magnet  is  lessened.  Soft  iron 
is  a  splendid  conductor  of  these  lines  of  force,  so  when 
the  core  is  in  place  the  "magnetic  flux,"  as  these  lines  are 
also  called,  can  rush  through  the  core  on  their  way  from 


ELECTROMAGNETISM  4! 

the  south  to  the  north  pole  of  the  electromagnet.  This 
reduces  the  air-trip  about  one-half  and  thus  greatly  in- 
creases the  strength  of  the  electromagnet. 

EXPERIMENT  25.    Polarity  of  coils. 

71.  Directions.  If  we  notice  the  direction  of  the  cur- 
rent as  it  passes  around  the  coil  to  see  whether  it  goes 
in  the  same  direction  as  that  taken  by  the  hands  of  a 
clock  or  in  the  opposite  direction,  we  shall  find  that  a 


Fig.  23 

certain  direction  of  current  always  produces  a  certain 
pole.  If  you  take  the  trouble  to  follow  this  up,  as  sug- 
gested in  Fig.  22,  you  will  find  that  when  the  current 
passes  in  a  right-handed  manner,  as  in  the  figure,  the 
left-hand  end  of  the  coil  will  be  a  south  pole.  If  you 
face  the  right-hand  end  of  the  coil,  the  current  is  seen 
(see  direction  of  the  arrows)  to  pass  around  it  in  an 
anti-clockwise  direction,  and  this  produces  a  north  pole. 

We  shall  want  to  know  what  pole  we  are  expected  to 
find  when  we  experiment  with  the  electromagnets  on 
motors,  so  the  student  should  fix  this  rule  thoroughly  in 
his  mind. 

EXPERIMENT  26.  About  horseshoe  electromag- 
nets. 

72.  Directions.    If  you  have  a  pair  of  electromagnets- 


42  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

already  wound  and  joined,  test  the  poles  with  a  compass- 
needle  to  see  if  one  pole  is  north  and  the  other  south. 
Also  note  the  way  in  which  the  current  enters  each  of 
the  magnets. 

73.  Discussion.  Fig.  23  shows  a  side  view  of  two 
electromagnets  with  the  wires  properly  joined  to  get  the 
best  results;  that  is,  they  are  so  wound  that  one  will  be 
north  and  the  other  south  when  the  current  passes,  as 
shown  by  the  arrow.  (See  "Electrical  Handicraft"  for 
full  details  for  making  different  kinds  of  electromag- 
nets.) 


Fig.  24 

If  you  notice  the  way  the  coils  are  wound,  and  also  the 
way  the  current  enters  the  coils,  you  will  find  that  when 
looking  down  upon  them,  as  in  Fig.  24,  a  north  pole  is 
produced  when  the  current  flows  through  the  wire  in  an 
anti-clockwise  direction,  and  that  the  pole  will  be  south 
when  it  flows  in  a  clockwise  direction.  This  was  men- 
tioned in  one  of  the  previous  experiments. 

EXPERIMENT  27.  Regarding  the  joining  of  elec- 
tromagnets. 

74.  Directions.  If  you  have  an  experimental  electro- 
magnet of  the  right  design,  you  can  try  the  strength  of 
the  two  when  arranged  as  suggested  in  Fig.  23,  and  then 
again  with  a  piece  of  iron  joined  to  the  lower  ends  of 
the  cores,  as  shown  in  Fig.  25.  Why  is  there  such  a  dif- 
ference in  the  strength? 


ELECTROMAGNETISM 


43 


75.  Discussion.  The  strips  of  iron  shown  in  Fig.  25 
are  held  firmly  between  the  base  and  the  ends  of  the 
cores,  thus  making  a  good  contact.  You  have  seen  that 
lines  of  force  find  it  much  easier  to  travel  through  iron 
than  through  the  air,  so  this  iron,  called  a  "yoke,"  makes 
a  complete  path  for  the  magnetic  flux  as  it  passes  from 
the  south  pole  to  the  north  pole.  At  this  point  the  lines 
of  force  pass  out  into  the  air  on  all  sides  of  the  magnet 
and  find  their  way  to  the  south  pole  near  by,  making  the 


Fig.  25 

field  of  force  very  strong  between  the  poles.  If  it  were 
not  for  the  yoke,  the  combination  would  be  much  weaker. 
This  fact  is  considered  in  the  construction  of  motors  and 
dynamos,  as  we  shall  soon  see.  The  yokes  should  be 
made  of  soft  iron,  and  for  students'  use  the  author  pre- 
fers yokes  that  are  made  up  of  a  number  of  strips. 
Fig.  25  shows  a  useful  size  for  experimental  magnets, 
full  size,  and  these,  are  shown  mounted  in  Fig.  26  (Ap- 
paratus No.  115  in  "Electrical  Handicraft").  A  careful 
study  of  ordinary  electromagnets  will  aid  you  in  seeing 
how  things  work  when  you  take  up  the  motors.  Fig.  27 
shows  a  larger  pair  of  mounted  magnets  arranged  es- 


44 


STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 


pecially  for  experimental  work  (Apparatus  No.  116  in 
"Electrical  Handicraft"). 

EXPERIMENT  28.    Magnetic  figure  of  electromag- 
nets. 

76.  Directions.    If  you  have  a  pair  of  electromagnets 
like  those  shown  and  discussed  in  the  last  experiment, 
arrange  a  sheet  of  glass  over  the  poles  by  laying  it  upon 
books ;  then  sprinkle  iron  filings  upon  the  glass  and  tap 
it,  as  previously  explained. 

77.  Discussion.     You  will  find  that  there  is  a  much 
stronger  field  between  the  poles  of  this  magnet  than  you 


Fig.  26 


Fig.  27 


had  in  the  case  of  the  permanent  horseshoe  magnet,  pro- 
vided you  have  any  kind  of  a  current,  and  that  you  have 
perfect  control  of  this  field  by  the  use  of  a  key  placed 
anywhere  in  the  circuit.  Notice  how  you  can  make  the 
field  disappear  when  you  open  the  circuit,  and  how  the 
lines  of  force  appear  the  instant  you  close  the  circuit. 

EXPERIMENT  29.  Magnetic  figure  of  single  elec- 
tromagnet. 

78.  Directions.  If  you  will  arrange  your  apparatus 
as  suggested  in  Fig.  28,  which  includes  a  battery,  or 
dynamo,  to  give  the  current,  a  key  and  a  single  magnet 
placed  on  its  side,  you  will  be  able  to  make  an  interest- 
ing magnetic  figure. 


ELECTROMAGNETISM 


45 


79.  Discussion.    This  shows  us  that  the  field  is  strong 
at  the  poles  of  the  electromagnet  and  that,  without  pole- 
pieces  or  other  additional  parts,  we  get  a  figure  much  like 
that  produced  by  a  straight  bar  magnet.    If  you  compare 
this  figure  with  that  of  the  pair  of  electromagnets,  you 
will  see  what  part  the  yoke  plays  in  saving  the  resistance 
to  the  lines  of  force. 

EXPERIMENT  30.     Magnetic  figure  of  two  like 
poles. 

80.  Directions.     If  you  have  a  pair  of  mounted  elec- 
tromagnets so  arranged  that  you  can  change  the  wiring 


Fig.  28 


Fig.  29 


(Fig.  27),  it  will  pay  you  to  join  them  up  so  that  the 
current  will  pass  around  them  in  the  same  direction ;  that 
is,  so  that  they  will  both  be  north  or  south  poles.  Do 
this,  then  make  the  magnetic  figure  of  this  combination 
and  see  whether  the  field  is  strong  or  weak  between  the 
poles. 

81.  Discussion.  When  the  two  poles  are  the  same,  the 
lines  of  force  repel  each  other,  thus  weakening  the  at- 
traction for  outside  pieces  of  iron.  This  arrangement  is 
not  adapted  for  use  in  motors  and  dynamos,  as  there  we 
want  as  strong  a  field  as  is  possible.  The  stronger  the 
field  between  the  poles  on  a  motor,  the  stronger  the  at- 
tractions and  repulsions  of  the  armature-magnets  for  the 
poles. 


CHAPTER  V 
MOTION  AND  CURRENTS 

EIGHT  EXPERIMENTS  SHOWING  HOW  MOTION   CAN  BE   I'RO- 
DUCED  BY  ELECTRIC  CURRENTS. 

EXPERIMENT  31.     Motion  produced  with  a  hol- 
low coil  of  wire  and  a  piece  of  soft  iron. 

82.  Directions.     Arrange  a  hollow  coil  of  wire,   as 
shown  in  Fig.  21,  then  suspend  a  short  length  of  soft 
iron  wire  by  means  of  a  piece  of  thread  directly  in  front 
of  the  opening.  Close  the  circuit  for  an  instant  and  see 
what  happens  to  the  wire. 

83.  Discussion.     We  have  here  what  might  be  called 
a  sucking  effect,  for  the  iron  wire  will  be  drawn  into  the 
coil   instantly.     We  have  a  polarizing  effect  upon  the 
iron  wire  as  soon  as  the  current  flows ;  then,  as  soon  as 
the  wire  gets  poles,   it  becomes   a  magnet  and   is   at- 
tracted  strongly  by   the   electromagnetism   of   the   coil. 
Even  by  this  simple  arrangement  we  can  produce  motion. 

EXPERIMENT  32.     Motion  produced  with  a  hol- 
low coil  of  wire  and  a  bar  magnet. 

84.  Directions.     In  place  of  the  iron  wire  of  the  last 
experiment,  use  a  magnetized  sewing-needle  and  see  the 
effect  when  the  poles  are  brought  near  the  hole  in  the 
coil.     Try  both  poles. 

85.  Discussion.    We  have  a  stronger  effect  than  in  the 
case  of  the  iron  wire,  because  the  magnetic  field  of  the 
small  permanent  magnet  is  stronger  than   that   of  the 
wire,  which  was  magnetized  by  induction,  and  which,  as 
has  been  explained,  has  but  little  retentivity.     The  fact 

46 


MOTION    AND   CURRENTS 


47 


that  one  end  of  the  needle  is  attracted  and  the  other  re- 
pelled by  the  coil,  shows  that  the  coil  has  a  particular 
pole  at  the  end  used. 

EXPERIMENT  33.  Motion  produced  with  an  elec- 
tromagnet and  a  piece  of  iron. 

86.  Directions.  Fig.  29  suggests  a  method  of  sup- 
porting your  electromagnet  H,  the  wires  IE  and  OE 
being  connected  to  a  key  and  battery.  1C  represents  a 


Fig.  30 

piece  of  iron,  which  should  be  held  a  short  distance  from 
H.  Try  the  effect  of  turning  the  current  on  and  off  at 
the  key. 

EXPERIMENT  34.    Motion  produced  with  an  elec- 
tromagnet and  a  bar  magnet. 

87.  Directions.     In  place  of  the  piece  of  iron  used  in 
the  last  experiment,  try  a  good  permanent  magnet.     See 
if  you  can  show  both  attractions  and  repulsions. 

EXPERIMENT  35.    Motion  produced  with  an  elec- 
tromagnet and  a  horseshoe  magnet. 

88.  Directions.      Fig.    30   shows   an    arrangement   by 
which,  with  the  reverser,  and  the  other  parts,  you  can 
get  some  interesting  results.     Try  reversing  the  current 
in  the  coil  until  you  get  the  best  results. 

89.  Discussion.    We  have,  in  this  experiment,  both  at- 
tractions  and   repulsions   in   rapid   succession,   and   this 
shows  what  takes  place  in  the  motor.     The  attractions 


40  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

and  repulsions  follow  each  other  very  rapidly  in  the  re- 
volving armatures,  but  of  course  the  motion  is  always 
in  one  direction  instead  of  in  opposite  directions,  as  in 
the  experiment. 

EXPERIMENT  36.  Motion  produced  with  two 
electromagnets. 

90.  Directions.  In  Fig.  31  we  have  two  electromag- 
nets, one  of  them  being  supported  in  such  a  manner  that 
it  will  swing  easily.  The  current  that  comes  from  the 


battery  branches  at  A  and  B,  so  as  to  magnetize  both 
coils  at  the  same  time.  Try  this  in  different  ways,  with 
the  poles  of  E  and  H  alike  and  unlike,  holding  E  in  the 
hand. 

91.  Discussion.     In  the  case  of  the  two  electromag- 
nets, we  have  the  main  parts  of  an  electric  motor  or 
dynamo.     We  see  from  this  that  we  can  get  an  attrac- 
tion or  a  repulsion  at  will,  depending  upon  the  poles  that 
are  near  each  other,  and  this  is  exactly  what  happens  in 
the  motor.    The  only  thing  lacking  here  is  some  plan  by 
which  we  can  automatically  turn  the  current  on  and  off. 

EXPERIMENT  37.    Rotary  motion  produced  with 
a  hollow  coil  and  a  permanent  magnet. 

92.  Directions.      If  you   will   now   refer   to   Fig.   21 
again,  you  will  find  that  by  this  plan  you  can  get  rotary 
motion  in  the  magnetic  needle  by  properly  turning  on 
and  off  the  current  at  the  reverser. 


MOTION   AND    CURRENTS  49 

93.  Discussion.    In  all  of  the  other  experiments  in  this 
chapter  we  produced  motion,  but  in  this  we  really  have 
a  rotary  motion,  and  it  is  this  that  we  want  in  the  regular 
motor. 

EXPERIMENT  38.    Rotary  motion  produced  with 
a  permanent  magnet  and  an  electromagnet. 

94.  Directions.     If  we  arrange  our  apparatus  as  sug- 
gested in  Fig.  32,  a  small  nail  wound  with  insulated  wire 
will  do  for  the  electromagnet,  and  have  a  key,  battery 


Fig.  32 

and  a  compass-needle,  we  can  get  rotary  motion  and 
regulate  it  pretty  well  by  turning  on  the  current  at  the 
right  time. 

95.  Discussion.  We  might  say  that  we  have  in  this 
apparatus  a  very  small  motor,  but  it  still  lacks  the  one 
important  feature  of  being  able  to  regulate  its  own  cur- 
rent. 


CHAPTER  VI 
ELECTRIC  MOTORS  IN  GENERAL 

96.  Simple  Action  of  Motors.    We  have  seen,  in  the 
numerous   experiments   that  have  been  suggested,  that 
motion  can  be  produced  in  many  ways  by  the  attractions 
and  repulsions  of  magnets — no  matter  whether  they  be 
permanent  magnets  or  electromagnets.  As  electromag- 
nets can  be  made  much  stronger  than  permanent  mag- 
nets, their  magnetism  being  under  perfect  control,  it  is 
evident  that  to  get  the  best  results,  we  need  a  current 
of  electricity  to  energize  the  coils  of  wire.     In  this  way 
we  can  get  powerful  magnets,  and  with  the  aid  of  pole- 
pieces  we  can  lead  the  magnetism  to  just  the  proper 
point.     Then,  by  a  plan  to  regulate  the  poles,  \ve  can 
get  either  attractions  or  repulsions  to  produce  a  constant 
rotary  motion. 

Now  that  we  have  mentioned  the  broad  principle  upon 
which  motors  work,  let  us  take  up  the  parts  of  a  simple 
motor  in  detail  to  learn  just  how  they  do  work. 

97.  The  Field-Magnets  on  all  ordinary  motors  do  not 
move,  as  they  are  generally  a  part  of  the  base  of  the 
machine.     There  are  many  forms  in  which  these  field- 
magnets  are  made,  depending  upon  the  design  of  the 
machine,  and  still  they  are  very  similar  to  each  other 
after  all.     When  we  speak  of  field-magnets,  we  really 
mean  the  whole  thing,  including  the  cores,  the  coils  and 
the  pole-pieces. 

When  a  current  passes  through  the  coils  of  the  field- 
magnets,  these  become  strong  electromagnets  and  they 
either  attract  or  repel  the  electromagnets  produced  in 


ELECTRIC    MOTORS   IN    GENERAL  51 

the  armature  by  the  same  current  or  by  a  part  of  the 
same  supplied  current.  Figs.  33,  34  and  35  show  three 
shapes  of  field-magnets  that  are  commonly  used  on  small 
motors,  and  although  the  second  looks  different  from 
the  first,  it  is  really  the  same  as  the  first,  but  tipped  upon 
its  side. 

In  Fig.  35,  however,  we  have  a  different  form,  in  which 
the  lines  of  force  have  two  paths  to  travel  on  their  way 
from  the  south  pole  through  the  two  yokes  Y  to  the 
north  pole.  This  form  of  field  is  like  that  discussed  in 
Experiment  20,  in  which  two  horseshoe  magnets  were 


Fig.  33  Fig.  34  Fig.  35 

used,  and  it  is  a  common  form  for  the  field-magnets  of 
large  motors  and  dynamos,  several  coils  and  pole-pieces 
being  used. 

In  the  three  illustrations  the  lettering  has  been  made 
the  same,  for  convenience,  in  which  C  stands  for  the  coil 
of  wire,  P  for  the  pole-pieces,  R  and  L  for  the  ends  of 
the  coils,  F  for  the  field  (where  the  lines  of  force  pass 
through  the  armature  when  it  is  in  place),  S  for  the 
space  between  the  ends  of  the  poles,  and  Y  for  the  yokes. 
In  these  drawings  all  parts  are  omitted  for  clearness,  ex- 
cept the  field-magnets. 

98.  Armatures  are  made  in  many  ways  with  as  many 
kinds  of  windings,  but  the  general  principle  is  the  same ; 
that  is,  coils  of  wire  magnetize  the  cores,  and  in  this  way 
we  get  electromagnets  that  attract  and  repel  the  field- 
magnets.  The  coils  of  wire  must  be  well  insulated  from 


52  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

the  iron  of  the  armature,  and  the  connections  must  be 
made  in  the  proper  way  to  give  the  desired  poles.  We 
shall  take  up  one  or  two  special  forms  of  armatures  when 
we  discuss  the  special  motors. 

99.  Commutators  are  devices  for  changing  the  direc- 
tion of  the  current  in  the  armature-coils  as  they  revolve, 
so  that  the  desired  poles  will  be  made.    These  consist  of 
bars  of  copper,  called  commutator  bars,  which  are  in- 
sulated from  each  other  and  from  the  shaft  of  the  ma- 
chine, but  so  fastened  that  they  will  turn  with  the  shaft. 
The  ends  of  the  armature-coils  are  joined  to  the  com- 
mutator bars  in  such  a  manner  as  to  allow  the  current 
to  enter  a  coil  from  one  bar  and  leave  it  by  way  of  one 
of  the  other  bars.     If  the  armature  did  not  revolve,  it 
would  be  an  easy  matter  to  get  the  current  in  and  out 
of  the  coils,  but,  as  we  must  have  a  constant  rotary  mo- 
tion, this  device  is  necessary. 

100.  The  Brushes  lead  the  current  to  the  commutator 
bars  and  thus  to  the  coils.     The  brushes  are  stationary 
and  gently  press  upon  the  commutator  as  it  revolves  with 
the  shaft.     Most  small  machines  have  but  two  brushes, 
which  feed  all  of  the  commutator  bars  as  they  revolve, 
current  entering  the  motor  through  one  brush  and  leav- 
ing by  the  other.     The  brushes  should  make  a  firm  con- 
tact with  the  commutator,  but  they  should  not  press  too 
hard  upon  it,  as  this  would  retard  the  motion  qf  small 
motors  on  account  of  too  much  friction. 

101.  Methods  of  Winding.     As  we  shall  see  in  some 
of  the  experiments  that  follow,  there  are  two  principal 
ways  in  which  small  motors  are  wound,  and  these  are 
called  the  "series"  and  the  "shunt"  windings.     Most  of 
the  smaller  motors  are  wound  by  the  series  method,  but 
some  of  those  that  are  a  little  larger  are  shunt-wound. 
The  smaller  motors  that  are  described  in  this  book  are 


ELECTRIC   MOTORS   IN    GENERAL  53 

so  designed  that  they  can  be  used  either  series-wound  or 
shunt-wound,  and  this  is  a  great  advantage  to  the  stu- 
dent when  it  comes  to  really  understanding  how  things 
work;  in  fact,  these  motors  have  been  arranged  in  this 
way  by  the  author  for  the  special  use  of  students.  (See 
experiments  for  discussions  of  these  two  methods.) 

102.  Reversing  Motors.     It  would  seem,  upon  first 
thought,  that  if  we  reverse  the  current  entering  a  small 
motor,  the  motor  should  reverse  at  once.     This  is  not 
the  case,  however,  as  we  shall  see  when  we  take  up  one 
of  the  small  motors  in  detail.     This  is  just  the  trouble 
with  all  of  the  ordinary  small  motors — for  they  are  not 
designed  so  that  they  can  be  reversed — and  when  we 
reverse  the  current  we  change  all  of  the  poles  in  both 
the  armature  and  field-magnets,  and  so  we  have  the  same 
effects  of  attractions  and  repulsions  as  before.    Wherever 
we  have  an  attraction  with  the  current  flowing  in  one 
direction,  we  again  get  an  attraction  with  the  current 
reversed,  and  this  makes  a  constant  rotation  in  the  one 
direction. 

To  get  the  motors  to  reverse,  we  must  have  them  so 
constructed  that  we  can  reverse  the  current  in  the  field, 
for  example,  without  reversing  it  in  the  armature.  This 
requires  some  form  of  reverser,  of  course,  so  connected 
with  the  motor  that  all  of  this  can  be  done.  When  we 
reverse  the  current  in  one  part  and  not  in  the  other,  we 
get  a  repulsion  where  we  previously  had  an  attraction, 
and  in  this  way  the  motor  has  to  turn  in  the  opposite 
direction.  (See  experiments  with  Motor  No.  I.) 

103.  Coils  in  "Series."     If  we  have  two  coils  of  wire 
arranged  as   indicated   in   Fig.   37  so  that  the  current 
which  passes  through  one  of  them  has  to  also  go  on 
through  the  other  before  it  can  return  to  the  battery,  we 
say  that  these  coils  are  in  series.     When  two  or  more 


54  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

coils  are  arranged  in  series,  the  resistance  of  all  of  them 
taken  together  is  equal  to  the  sum  of  their  separate  re- 
sistances, for  the  same  current  has  to  go  through  all  of 
them,  one  after  the  other. 

104.  Coils  in  "Shunt."  In  Fig.  38  we  have  two  coils 
so  arranged  that  the  current  coming  from  any  source 
branches  into  two  different  parts  at  C,  one  part  return- 


F 

Fig.  37  Fig.  38 

ing  to  Z  through  coil  F,  and  the  other  part  through  coil 
A.  We  say  that  these  two  coils  are  in  "parallel,"  or 
that  one  of  them  is  a  "shunt"  of  the  other.  A  shunt 
is,  really,  a  branch,  and  when  a  wire  branches  into  two 
or  more  parts,  each  branch  gets  a  part  of  the  current  and 
the  resistance  of  all  of  the  branches  together  is  less  than 
that  of  any  of  the  branches  alone.  When  the  branches 
are  all  carrying  current,  the  electricity  has  more  than 
one  path,  or,  in  other  words,  there  is  more  copper  to 
carry  it. 


CHAPTER  VII 
PRACTICAL  EXPERIMENTS  WITH  MOTORS 

105.  Small   Motors.     There  are  many  good  motors 
upon  the  market,  but  space  will  not  permit  of  a  descrip- 
tion of  all  of  them,  and  as  the  general  principles  are  the 
same  in  all  of  them,  so  many  details  will  not  be  neces- 
sary.    In  the  experiments  which  follow,  the  author  has 
chosen  small  motors  that  seem  to  him  to  be  best  adapted 
to  the  use  of  students,  some  of  the  motors  being  those 
already  upon  the  market,  and  some  being  of  special  de- 
sign to  make  them  more  useful  to  the  student;  for  it  is 
not  enough  to  have  a  motor  that  will  simply  go  around, 
when  it  comes  to  experimental  work. 

All  of  the  motors  described  herein  are  made  of  the 
best  materials  by  skilled  workmen,  thus  giving  us  some- 
thing upon  which  we  can  depend,  and  wyhere  special  de- 
signs have  been  given,  we  have  something  that  will  do 
all  that  ordinary  motors  will  do,  and  more  besides. 

As  the  motors  used  for  these  experiments  differ  some- 
what in  shape  and  construction,  and  as  we  shall  have  to 
refer  to  them  frequently,  it  has  been  thought  best  to  give 
them  numbers  and  to  refer  to  them  by  these  numbers. 
Some  of  the  motors  can  be  used  as  dynamos,  and  this 
is  a  great  advantage  for  the  student;  for  he  then  really 
has  two  machines  in  one.  (See  Chap.  9.) 

106.  Motor  No.  1.    This  motor  (Fig.  39)  is  designed 
for  students  and  others  who  want  a  small  motor  for  ex- 
perimental purposes,  as  well  as  for  all  of  the  regular 
work  that  any  small  motor  can  do.     After  considerable 

55 


56  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

experimenting,  the  author  decided  that  this  would  be  the 
best  form  and  construction  for  an  all-around  small  motor, 
and  he  believes  that  it  can  be  used  in  more  ways  than 
any  other  motor  of  equal  cost.  It  is  an  efficient  motor 
for  its  size,  and  it  gives  a  very  good  idea  of  the  general 
construction  and  action  of  large  motors.  One  of  the 
special  features  of  this  motor  is  that  it  is  so  designed 
that  it  can  be  used  on  a  circuit  with  a  current-reverser, 
rheostat,  etc.,  thus  making  it  possible  to  regulate  the 
direction  of  rotation  and,  besides,  to  control  the  speed 
while  running  in  either  direction. 

This  change  of  direction  and  regulation  of  speed  is  of 
the  greatest  value  when  you  want  to  run  small  toys  and 
various  mechanical  effects.  The  four  nickel-plated  bind- 
ing-posts are  mounted  upon  the  framework  of  the  motor, 
and  not  upon  the  wooden  base,  as  is  usually  the  case,  so 
that  the  motor  itself  can  be  removed  from  the  base  and 
used  in  different  ways,  remounting  it  upon  toys,  etc.  In 
this  way  it  will  still  retain  the  ability  to  reverse. 

As  it  has  a  three-pole  armature,  it  will  start  promptly 
as  soon  as  the  current  is  turned  on.  The  armature-shaft 
carries  a  pulley,  and  it  is  so  arranged  that  a  fan  can 
be  put  on  without  removing  the  pulley.  One  cell  of 
battery  will  run  this  motor  at  high  speed,  but  it  will 
be  found  best,  especially  where  you  want  to  run  toys  or 
the  fan,  to  arrange  the  batteries  according  to  the  re- 
quirements, thus  reducing  the  strain  on  the  cells  and  in- 
creasing their  life  considerably.  (See  Chap.  10.) 

Motor  No.  i  stands  three  and  one-half  inches  high.  It 
is  finished  in  black  enamel  with  nickel-plated  trimmings, 
and  it  is  well  made  and  strong.  With  it  are  furnished 
one  long  and  two  short  nickel-plated  brass  connecting- 
straps,  with  which  various  connections  can  be  conve- 
niently made  for  the  experiments. 


PRACTICAL   EXPERIMENTS    WITH    MOTORS  5/ 

107.  Taking  Motor  No.  1  Apart.  In  order  to  make  a 
study  of  this  motor,  all  that  is  necessary  is  to  remove  the 
armature ;  and  to  do  this  simply  take  out  the  two  small 
screws  that  hold  the  strap-bearing  at  the  pulley-end  of 
the  shaft,  this  being  called  the  back  bearing-strap.  Care- 
fully pull  the  armature  out  and  put  the  screws  back  in 
place  so  as  not  to  lose  them.  In  replacing  the  armature, 


Fig.  39 

be  very  careful  not  to  bend  the  brushes  and  to  so  center 
the  armature  when  putting  in  the  screws  that  it  will 
turn  freely.  This  must  be  done  with  care  or  the  arma- 
ture can  not  revolve  as  it  should,  and  it  may  even  hit 
upon  the  field-magnets  as  it  turns. 

EXPERIMENT  39.  To  test  for  poles  of  the  field- 
magnets. 

108.  Directions.  Following  the  directions  in  para- 
graph 107,  remove  the  armature  of  Motor  No.  i  and 
arrange  it  in  circuit  with  a  reverser  and  a  dry  battery,  as 
in  Fig.  40,  being  careful  to  have  your  connections  as 
shown.  As  previously  explained,  the  current  coming 


58  STUDY  OF  ELECTRIC  MOTORS  BY  EXPERIMENT 

from  the  carbon  of  the  cell  cannot  get  beyond  the  re- 
verser  until  one  of  the  keys  is  pressed. 

Hold  a  compass-needle  near  one  of  the  pole-pieces  and 
then  near  the  other  as  you  press  the  left-hand  key  of 
the  reverser  for  a  moment,  and  note  which  pole-piece  at- 
tracts the  north  pole  of  the  compass-needle.  When  you 
have  decided  which  pole-piece  is  a  north  pole,  repeat  the 
experiment  and  press  the  right-hand  key  of  the  reverser. 

109.  Discussion.  The  student  should  note  that  when 
the  current  enters  the  left-hand  binding-post  it  passes 
through  the  coil  in  a  clockwise  direction  as  you  face  the 
left-hand  end  of  the  coil,  and  in  an  anti-clockwise  direc- 


Fig.  40 

tion  when  you  reverse  it.  From  the  results  a  comparison 
should  be  made  with  Experiment  25.  We  have  here  a 
good  example  of  pole-pieces,  which  lead  the  lines  of  force 
up  from  the  ends  of  the  coil  to  a  place  where  they  can 
stream  through  the  armature-core  when  it  is  in  place. 

EXPERIMENT  40.    To  test  for  residual  magnetism 
in  the  pole-pieces. 

110.  Directions.     Having  performed  Experiment  39, 
test  the  poles  for  magnetism  without  passing  any  current 
through  the  coil. 

111.  Discussion.    The  iron  used  in  the  construction  of 
motors  and  dynamos  holds  some  of  the  magnetism  after 
the  current  ceases  to  flow,  as  is  shown  by  this  experi- 
ment ;  in  fact,  if  this  were  not  the  case,  the  dynamo  could 
not  start  to  generate  a  current  as  soon  as  it  is  revolved. 
This  will  be  taken  up  more  fully  in  "The  Study  of  Dyna- 
mos by  Experiment." 


PRACTICAL   EXPERIMENTS  WITH    MOTORS  59 

EXPERIMENT  41.    To  test  the  lifting-power  of  the 
field-magnets. 

112.  Directions.     With  the  armature  removed,  as  in 
the  above  experiments,  and  as  shown  in  Fig.  41,  see  if 
you  can  lift  the  armature  when  you  press  one  of  the  keys 
of  the  reverser.     Try  other  pieces  of  iron,  letting  the 
current  pass  for  a  moment  only,  so  as  not  to  overwork 
the  cell. 

EXPERIMENT  42.     To  test  the  lifting-power  of 
the  field-magnets  when  the  armature  is  in  place. 

113.  Directions.     Slip  the  armature  back  into  place 
without  screwing  on  the  bearing,  and  again  test  the  lift- 


Fig.  41 

ing  power,   comparing  it   with   the   results   of   Experi- 
ment 41. 

114.  Discussion.    It  is  evident  that  when  the  armature 
is  in  place  the  lifting-power  is  small,  and  from  the  pre- 
vious discussions,  we  come  to  the  conclusion  that  there 
are  not  so  many  lines  of  force  leaking  into  the  air  now 
as  there  were  when  the  armature  was  out  of  the  field. 
Let  us  study  this  more  fully  in  the  next  experiment. 

EXPERIMENT  43.     To  study  the  magnetic  field 
of  the  field-magnets  with  the  armature  in  place. 

115.  Directions.    Arrange  your  apparatus  as  shown  in 
Fig.  42,  holding  the  base  of  the  motor  in  a  small  vise. 
In  this  way  the  pole-pieces  can  be  used  to  hold  a  piece 
of  cardboard  in  a  horizontal  position,  and  all  can  be  held 


60  STUDY  OF  ELECTRIC  MOTORS  BY  EXPERIMENT 

firmly  if  the  two  little  screws  that  usually  fasten  the 
bearing-strap  be  put  through  small  holes  in  the  cardboard 
and  screwed  into  place.  A  small  slit  will  be  necessary  to 
allow  the  cardboard  to  be  pushed  beyond  the  shaft  be- 
tween the  pulley  and  the  nickel-plated  bearing-strap.  A 
small  piece  of  paper  can  be  pasted  over  the  slot  when  the 
cardboard  is  in  place,  to  keep  the  filings  from  falling 
through,  and  the  bearing-strap  may  be  turned  out  of  the 
way.  Make  the  magnetic  figure  of  the  field  with  iron 
filings,  tapping  the  cardboard  as  previously  explained. 


Fig.  42  Fig.  43 

EXPERIMENT  44.  To  test  the  magnetic  field  of 
the  field-magnets  with  the  armature  removed. 

116.  Directions.    Arrange  as  for  the  last  experiment, 
but  with  the  armature  removed,  and  again  make  the  mag- 
netic figure  with  filings. 

117.  Discussion.     From  the  last  two  experiments  it 
is  evident  that  the  magnetic  field   of  a  pair  of  field- 
magnets  like  that  on  Motor  No.  I  is  more  evident  when 
the  armature  is  removed,  because  the  lines  of  force  pass 
through  the  iron  of  the  armature  more  easily  than  through 
the  air;  and,  when  the  armature  is  there,  the  lines  of 
force  merely  have  to  jump  across  the  small  air-gaps. 

When  the  armature  stands  still,  the  lines  of  force  pass 
nearly  straight  through  the  iron  core,  following  the 
easiest  path.  When  the  armature  is  revolving  and  the 


PRACTICAL   EXPERIMENTS    WITH    MOTORS  6l 

motor  is  running  regularly,  these  lines  of  force  are 
slightly  changed  in  their  course,  but  this  need  not  be 
taken  into  account  in  these  small  motors. 

The  chief  thing  to  keep  in  mind  is  that  the  thousands 
of  lines  of  force  are  threading  through  the  armature  and 
its  coils  when  they  revolve,  and  that  if  this  were  not  the 
case  the  motor  would  not  revolve  and  the  dynamo  would 
not  generate  a  current. 

EXPERIMENT  45.  Making  permanent  magnets 
with  the  motor. 

118.  Directions.      With    the    field-magnets    you    can 
make  small  permanent  magnets  out  of  pieces  of  steel, 
needles,  etc.,  if  you  allow  the  current  to  pass  through  the 
coil,  the  armature  being  removed. 

Various  other  experiments  can  be  done  with  these 
electromagnets,  but  some  sort  of  a  key  should  be  in  the 
circuit  so  that  the  current  can  be  regulated,  leaving  it 
on  but  for  a  moment  each  time  to  save  the  battery. 

EXPERIMENT  46.  To  test  the  armature  for  mag- 
netism. 

119.  Directions.      Remove    the    armature    of    Motor 
No.  i  and  slip  the  pulley-end  of  the  shaft  into  the  hole 
in  the  front  bearing-strap,  as  shown  in  Fig.  43.     With 
books  or  blocks  build  up  a  little  platform  under  the  core 
of  the  armature  so  that  you  can  place  nails  or  other 
small  pieces  of  iron  near  the  core.    Hold  one  of  the  wires 
from  a  battery  upon  one  of  the  commutator  bars,  and 
with  the  other  hand  touch  the  remaining  wire  to  the 
other  two  bars  in  succession  to  see  if  the  electromagnets 
of  the  armature  can  lift  iron. 

120.  Discussion.    From  this  it  is  evident  that  the  elec- 
tromagnets produced  by  a  current  passing  through  the 
armature-coils  are  quite  strong,  and  that  they  are  capable 
of  creating  a  decided  pull  upon  pieces  of  iron.     It  must 


62  STUDY  OF  ELECTRIC  MOTORS  BY  EXPERIMENT 

also  be  evident  that  if  xthe  field-magnets  are  properly 
magnetized,  the  pull  will  be  still  greater. 

EXPERIMENT  47.  To  test  the  armature-magnets 
for  poles. 

121.  Directions.  Arrange  your  apparatus  as  directed 
for  the  above  experiment,  but  instead  of  trying  to  lift 
iron  when  the  current  is  turned  on,  make  the  little  plat- 
form tall  enough  to  hold  your  compass-needle  near  the 
poles. 

Part  1.  Place  the  armature,  as  shown  in  Fig.  44, 
which  gives  merely  the  end  view,  so  that  the  pole  con- 


Fig.  44 

taining  the  small  screw  will  be  on  top.  This  should  be 
done  for  convenience,  as  the  screw  will  act  as  a  guide 
and  enable  you  to  keep  the  facts  clear.  In  this  a  battery 
is  shown  to  the  right,  the  wire  from  the  zinc  being 
marked  Z  and  that  from  the  carbon  C.  The  current 
coming  from  the  cell  by  way  of  wire  C,  called  the  posi- 
tive wire,  will  enter  the  commutator  bar  at  the  top, 
marked  T,  and  return  to  the  cell  through  the  right  bar, 
marked  R.  Test  each  pole  of  the  armature,  following 
the  current  in  your  mind,  and  see  if  the  law  given  in 
Experiment  25  holds  true,  remembering  that  the  current 
does  not  pass  around  all  of  the  cores  in  a  clockwise  di- 
rection. Make  a  diagram  and  mark  your  results. 

Part  2.  Turn  the  armature  to  the  right  through  one- 
third  of  a  revolution,  which  will  bring  pole  I  over  to 
the  former  position  of  pole  2,  and  so  on  around.  Test 


PRACTICAL   EXPERIMENTS    WITH    MOTORS  63, 

again,  still  touching  wire  C  to  the  top  bar,  and  note  that 
changes  have  been  made  in  two  of  the  poles,  although 
the  relative  positions  of  the  north  and  south  poles  have 
remained  the  same. 

Part  3.  Repeat  Part  2,  again  turning  the  armature 
one-third  of  a  revolution.  Do  the  same  relative  positions 
remain  ? 

Part  4.  Repeat  the  above,  reversing  the  current ;  that 
is,  let  the  wire  from  Z  touch  the  top  bar,  and  that  from 
C  the  right  bar.  Make  a  diagram  of  the  new  poles  and 
compare  the  results  with  those  above. 

122.  Discussion.  If  the  student  will  take  the  trouble 
to  do  the  above  experiment  carefully  and  fix  the  results 
in  his  mind,  he  will  have  no  chance  to  forget  the  general 
principles  upon  which  the  current  reverses  each  half  revo- 
lution through  the  coils  of  the  little  armature  of  Motor 
No.  i.  As  the  current  is  supposed  to  pass  through  the 
motor  in  one  direction,  when  it  is  running  under  ordi- 
nary conditions,  it  must  be  clear  that  while  the  pole- 
pieces  of  the  field-magnets  have  constant  polarity,  the 
three  poles  of  the  armature  are  rapidly  changing. 


CHAPTER  VIII 

SPEED  REGULATION  AND  DIRECTION  OF 
ROTATION 

EXPERIMENT  48.    Direction  of  rotation. 

123.  Directions.  Part  1.  Assemble  the  motor  again, 
being  careful  not  to  bend  the  brushes  and  to  have  the 
armature  run  easily  without  hitting  the  field-magnets. 
This  is  important,  and  it  is  best  to  put  a  small  drop  of 
machine,  oil  on  each  bearing,  placing  it  with  a  toothpick 
or  a  match.  With  the  apparatus  arranged  as  in  Fig.  40, 
but  without  connecting  the  field-coils  to  those  of  the 
armature,  press  the  right-hand  key  of  the  reverser  .to 


Fig.  45 

allow  the  current  to  enter  the  coil  at  the  right  end ;.  that 
is,  allow  the  current  to  pass  through  the  coil  in  a  clock- 
wise direction  as  you  look  at  it  from  the  right.  Test  the 
pole  again  and  satisfy  yourself  with  the  compass-needle 
that  the  right-hand  pole  is  south.  You  may  even  omit 
the  reverser  and  touch  the  wire  from  the  carbon  to  the 
right-hand  binding-post  of  the  field,  with  the  wire  from 
the  zinc  to  the  other  post  on  the  field. 

Part  2.  With  the  long  connecting-strap  join  the  left- 
hand  post  of  the  field  across  to  the  right-hand  post  of  the 
armature,  as  shown  in  Fig.  45,  but  before  you  turn  on 

64 


SPEED  REGULATION  AND  DIRECTION  OF  ROTATION        65 

the  current,  try  to  figure  out  which  way  the  motor  should 
run  if  the  wire  from  the  carbon  (the  positive  wire) 
should  let  the  current  in  at  R,  from  which  it  would  go 
through  the  field-coil  to  L,  across  to  B,  thence  through 
the  armature-coils  to  A  and  back  to  the  battery.  When 
you  have  decided,  see  if  you  were  right  by  trying  with 
the  current. 

124.  Discussion.     Keeping  in  mind  the  fact  that  the 
right-hand  pole-piece  of  the  field  should  be  south,  and 
that  as  the  current  enters  the  top  commutator  bar,  as  in 
Experiment  47,  Part  I,  making  the  top  pole-piece  of  the 
armature  also  south,  there  will  be  a  repulsion  between 
these  two  parts,  and  the  motor  will  turn  forwards ;  that 
is,  away  from  the  brushes,  giving  it  an  anti-clockwise 
direction  when  you  face  the  armature. 

We  have  already  mentioned  the  fact  that  the  motor 
will  run  in  the  same  direction  as  before  if  we  reverse  the 
current  in  the  whole  motor,  as  we  shall  do  if  we 
simply  change  the  wires  leading  from  the  battery.  The 
reason  should  now  be  clear,  for  in  this  case  the  right 
pole  of  the  field  will  be  north,  and  so  will  the  top  pole- 
piece  of  the  armature.  The  poles  being  the  same,  that 
is,  north,  we  get  a  repulsion  as  before.  The  previous 
experiments  showed  that  the  poles  are  reversed  when  the 
current  reverses. 

125.  Attractions  and  Repulsions  in  Motor  No.  1.  We 
have  just  shown  that,  with  certain  connections,  we  have 
a  south  pole  at  the  right  of  the  motor  and  also  a  south 
pole  at  the  top  of  the  armature,  thus  causing  a  repulsion. 
The  student  must  not  get  the  idea  from  this  that  we  have 
only  repulsions.    We  arrived  at  the  conclusions  about  the 
repulsion  by  considering,  for  convenience,  but  one  pole 
of  the  armature.     In  Experiment  47  we  found  that  the 
two  side  poles  of  the  armature  were  north  when  the  top 


66  STUDY  OF  ELECTRIC   MOTORS  BY   EXPERIMENT 

pole  was  south,  and  so  we  have  quite  a  number  of  at- 
tractions and  repulsions. 

As  will  be  seen  by  referring  to  Fig.  46,  the  top  pole 
of  the  armature  is  repelled  by  the  right  field-pole,  and  it 
is  at  the  same  time  attracted  by  the  left  field-pole.  Again, 
the  left  and  right  poles  of  the  armature  are  repelled  by 
the  left  pole  of  the  field,  and  both  are  attracted  by  the 
right  field-pole.  With  the  numerous  attractions  and  re- 
pulsions, we  get  a  steady  pull  and  push  in  the  same  di- 
rection. 

Now,  of  course,  if  the  poles  of  the  armature  remained 
the  same  during  the  entire  revolution,  the  armature  would 
soon  find  a  position  in  which  its  poles  would  have  the 


Fig.  46 

greatest  attraction  for  the  poles  of  the  field,  and  there  it 
would  remain.  Here  is  where  the  commutator  does  its 
work,  by  reversing  the  current  as  the  brushes  change  to 
other  commutator  bars,  thus  keeping  up  the  motion.  If 
you  look  carefully  at  the  commutator-end  of  the  arma- 
ture, you  will  see  that  this  change  is  made  just  as  the 
right  pole  of  the  armature  reaches  the  middle  point  of 
the  south  field-piece.  This  instantly  changes  the  attrac- 
tion to  a  repulsion.  If  you  slowly  turn  the  armature  and 
watch  for  this,  you  will  see  that  all  of  the  changes  are 
made  at  this  point,  for  the  lower  brush  then  slides  from 
the  right  commutator  bar  to  the  left  one.  The  above 
applies,  of  course,  when  the  experiment  is  performed  as 
described  above. 


SPEED  REGULATION  AND  DIRECTION  OF  ROTATION        67 

EXPERIMENT  49.     Backward  motion  for  Motor 
No.  1. 

126.  Directions.    Put  on  one  of  the  short  connecting- 
straps,  CS,  so  that  it  will  join  binding-posts  R  and  B, 
as  shown  in  Fig.  47,  then  connect  the  positive  wire, 
from  a  batten'  to  L  and  the  negative  wire  to  A.  The  cur- 
rent will  now  pass  through  the  field  in  the  opposite  and 
through  the  armature  in  the  same  direction  as  in  the  last 
experiment ;  that  is.  we  have  reversed  the  current  in  the 
field  without  reversing  it  in  the  armature,  and  this  makes 
the  motor  revolve  in  a  clockwise  direction. 

127.  Discussion.    This  plan  of  reversing  the  motor  is 


Fig.  48 

rather  unhandy,  as  it  is  not  convenient  to  change  the 
wiring  every  time  we  want  to  reverse  the  motor;  so  we 
make  use  of  the  current-reverser  to  do  this  for  us,  as 
directed  below. 

EXPERIMENT  50.     Reversing  Motor  No.  1  with 
the  current-reverser. 

128.  Directions.    Arrange  the  motor,  a  battery  and  a 
current-reverser,  as  shown  in  Fig.  48.     Press  the  right- 
hand  key  first  and  see  if  the  motor  turns  in  the  same 
direction  as  in  Experiment  48 ;  that  is,  anti-clockwise. 
Follow  the  current  in  your  mind  to  make  sure  that  this 
is  correct,  then  press  the  left-hand  key  for  a  moment  to 
see  if  the  motor  reverses. 

129.  Discussion.    We  have,  in  this  case,  a  method  of 
easily  accomplishing  the  results  shown  in  the  previous 


68 


STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 


experiment,  and  this  explains  the  general  method  used, 
even  in  large  motors.  The  main  point  to  be  remembered 
is,  that  in  reversing  the  motor  we  have  to  reverse  the 
current  in  either  the  field  or  the  armature  without  re- 
versing it  in  the  other. 

EXPERIMENT  51.  Reversing  Motor  No.  1  by  a 
second  method. 

130.  Directions.  Arrange  the  wiring  as  shown  in  Fig. 
49,  in  which  the  reversing  will  take  place  in  the  arma- 
ture-coils, connecting  the  field-coil  up  as  you  did  the 


Fig.  49 

armature  in  the  previous  experiment.     See  if  you  still 
get  the  same  reversing  as  before. 

131.  Discussion.    We  see  from  this  that  the  motor  re- 
verses by  this  plan  as  well  as  by  the  other.     Now  that 
we  have  succeeded  in  changing  the  direction  of  rotation 
of  this  little  motor,  let  us  see  how  we  can  regulate  its 
speed. 

EXPERIMENT  52.    Regulation  of  speed  for  Motor 
No.  1,  coils  in  series. 

132.  Directions.    Arrange  the  motor,  rheostat  and  bat- 
teries, as  shown  in  Fig.  50,  then  try  the  speed  at  various 
points  on  the  rheostat. 

133.  Discussion.     In  this  case,  we  see  that  the  cur- 
rent goes  through  the  rheostat,  the  field-coil,  the  con- 
necting-strap, and  then  through  the  armature-coils  and 
back  to  the  batteries.     There  are  no  branches  here  to 
divide  the  current,  so  we  say  that  we  have  a  series-wound 


SPEED  REGULATION  AND  DIRECTION  OF  ROTATION        69 

motor.  In  this  experiment  we  can  use  the  five-point  rheo- 
stat, as  shown  with  two  batteries,  or  the  eleven-point 
rheostat  with  three  batteries.  These  instruments  are  de- 
scribed in  Chapter  3. 

EXPERIMENT  53.  Controlling  speed  and  direc- 
tion of  rotation  of  Motor  No.  1,  series- wound. 

134.  Directions.  Fig.  51  shows  how  to  connect  the 
reverser  with  the  other  things  used  in  the  last  experi- 
ment. Be  sure  that  you  get  the  connections  right  and 


Fig.  50 

then  try  to  vary  the  speed  with  the  rheostat  and  the  di- 
rection of  rotation  with  the  reverser.  (See  Sec.  137  on 
Series-wound  Motors.) 

135.  Discussion.     It  will  be  seen  here  that  the  coils 
are  still  in  series,  even  if  the  reverser  be  used,  and  that 
we  can  change  the  speed  of  the  motor  when  it  is  running 
in  either  direction.     This  arrangement  is  a  very  handy 
one  for  running  toys,  as  we  have  the  motor  under  perfect 
control.     (See  the  author's  "Real  Electric  Toy-Making 
for  Boys"  for  various  toys  that  are  to  be  run  with  small 
motors.) 

136.  Load  on  Motors.    When  a  motor  is  running  with- 
out doing  work  and  simply  has  to  turn  itself,  we  say  that 
it  has  no  load.    Although  the  motor  has  no  outside  work 
to  do  in  this  case,  it  really  has  something  to  do,  for  it 
must  overcome  the  friction  of  its  bearings  and  the  re- 
sistance of  the  air  to  its  rapidly  revolving  armature. 

As  soon  as  we  attach  it  to  some  machine  and  make  it 


7O  STUDY  OF  ELECTRIC   MOTORS   BY  EXPERIMENT 

do  outside  work,  we  say  that  the  motor  is  running  with 
a  load,  and  it  would  seem  perfectly  natural  for  a  motor 
to  slow  down  a  little  when  its  load  is  increased.  From 
this  we  should  also  expect  that  the  current  would  have 
to  be  increased  to  keep  up  the  proper  speed  with  the 
larger  load. 

Small  motors  do  not  run  well  at  slow  speed,  and  so 
we  have  to  gear  them  down  to  get  to  the  proper  speed 
for  toys  and  other  things.  (See  "Real  Electric  Toy- 
Making  For  Boys,"  Chaps.  10,  11,  12,  for  full  direc- 


Fig.  51 

tions  for  making  shafting,  bearings,  pulleys,  winding- 
drums,  etc.,  for  small  motors.) 

137.  Series-Wound  Motors.  As  has  just  been  men- 
tioned, it  is  natural  to  expect  that  a  motor  should  run 
faster  as  soon  as  its  load  is  decreased,  and  still  faster 
when  the  load  is  entirely  thrown  off.  In  the  case  of  the 
series-wound  motor,  this  would  become  a  serious  thing 
if  it  were  not  watched  and  its  speed  regulated,  for  these 
motors  have  a  tendency  to  keep  on  running  faster  and 
faster,  or  to  "race,"  as  it  is  called,  and  such  motors  have 
been  known  to  actually  tear  themselves  to  pieces  by  the 
excessive,  speed  under  no  load. 

In  places  where  it  might  be  possible  for  the  belts  to 
break  or  come  off,  thus  allowing  a  series-wound  motor 
to  race,  or  where  a  variable  speed  is  not  wanted,  series- 
wound  motors  are  not  generally  used.  There  are  many 
places,  however,  where  a  variable  speed  is  really  wanted, 


I 
SPEED  REGULATION  AND  DIRECTION  OF  ROTATION        ?! 

as,  for  example,  on  electric  cars,  pumps,  hoists,  etc.,  and 
in  these  cases  the  speed  is  under  the  control  of  a  rheostat 
placed  in  the  main  circuit,  as  in  one  of  the  previous  ex- 
periments. For  work  like  this,  the  operator  is  on  hand 
to  attend  to  the  rheostat.  In  the  case  of  ordinary  elec- 
tric fans,  for  example,  the  load  is  constant,  and  there  is 
no  chance  for  the  fan  to  race,  and  so  many  of  these  motors 
are  series-wound.  They  will  race,  however,  if  you  re- 
move the  fan  and  let  them  run. 

In  series-wound  motors,  the  same  current  passes 
through  both  armature  and  field,  so  when  the  strength  of 
current  in  either  of  these  two  parts  is  changed,  it  is  also 
changed  in  the  other  part.  For  example,  if  we  increase 
the  load  on  the  motor,  the  armature  will  naturally  slow 
down  a  little,  and  from  the  experiments  on  counter-elec- 
tromotive force,  we  know  that  the  resistance  of  the  arma- 
ture will  be  decreased.  This  will  allow  more  current  to 
pass  through  the  armature,  and  we  should  expect  that 
more  power  would  be  the  result ;  but,  as  mentioned  above, 
the  field  also  feels  the  effect  of  this  increased  current,  and 
the  magnetic  flux  of  the  field  is  increased.  The  counter- 
electromotive  force  in  the  armature  increases  with_  the 
additional  magnetic  flux,  and  so  the  motor  has  to  slow 
down. 

The  thing  may  be  summed  up,  in  a  general  way,  by 
saying  that  the  strength  of  the  field  is  not  constant  in 
series-wound  motors.  Every  change  in  load  makes  a 
corresponding  change  in  the  strength  of  the  field  and  in 
the  pressure  of  the  counter-electromotive  force. 

This  trouble  is  overcome  in  shunt-wound  motors,  as 
will  be  explained  below.  Series-wound  motors  have  a 
very  strong  pulling  power  or  "torque"  when  they  start, 
and  this  is  an  advantage  in  starting  electric  cars  and 
other  machinery  for  which  they  are  adapted. 


72  STUDY  OF  ELECTRIC  MOTORS  BY  EXPERIMENT 

EXPERIMENT  54.    Motor  No.  1,  shunt-wound. 

138.  Directions.    Place  the  two  short  connecting-straps 
upon  the  motor,  as  shown  in  Fig.  52,  then  hold  the  ends 
of  the  wires  from  a  battery  against  the  straps  to  see  if 
the  motor  will  turn. 

139.  Discussion.     By  this  method  of  wiring,  the  cur- 
rent which  passes  to  strap  i  will  divide,  part  of  it  going 
through  the  field-coil  and  the  rest  through  the  armature- 
coils  to  strap  2  and  back  to  the  battery.     While  Motor 
No.  I  is  not  wired  for  a  shunt-wound  motor,  it  works 
well  enough  for  experimental  purposes.     Some  of  the 


larger  motors  to  be  described  later  are  so  wound  that 
they  really  work  better  as  shunt-wound  motors  than  they 
would  if  connected  up  as  series-wound  motors. 

EXPERIMENT  55.  Motor  No.  1,  shunt-wound  and 
reversible,  with  one  method  of  speed  regulation. 

140.  Directions.  Fig.  53  shows  one  way  to  wire  your 
apparatus  to  get  the  results  secured  in  large  motors ;  that 
is,  to  have  them  shunt-wound,  and  at  the  same  time  to 
have  them  reversible  and  under  control  as  to  speed.  In 
this  diagram  are  shown  the  motor  without  any  connect- 
ing-straps, a  three-cell  battery,  the  reverser,  and  the 
eleven-point  rheostat,  all  of  which  have  been  described 
in  Chapter  3. 

With  this  wiring,  care  must  be  taken  not  to  short-cir- 
cuit the  batteries  through  the  armature  and  rheostat,  for 
the  current  can  go  this  way  without  producing  motion  in 
the  motor.  If  care  be  used,  there  will  be  no  trouble 
from  this,  but  it  is  best  to  put  a  one-point  switch  in 


SPEED  REGULATION  AND  DIRECTION  OF  ROTATION        73 

wire  i  and  to  open  this  every  time  the  motor  is  to  be 
stopped ;  and  the  switch-arm  of  the  rheostat  should  be 
turned  to  the  dead-point,  as  shown.  The  keys  of  the 
reverser  will  prevent  a  short  circuit  through  the  field- 
coil,  as  the  current  can  not  pass  unless  one  of  the  keys 
is  pressed.  Work  out  the  diagram  in  your  mind  before 
doing  the  actual  experiment. 

141.  Discussion.  The  above  arrangement  is  what  we 
may  have  in  large  motors,  although  there  are  certain  dis- 
advantages. The  student  should  thoroughly  fix  in  his 


Fig.  53 


mind  that  we  are  reversing  on  the  field  and  regulating 
the  speed  by  means  of  resistance  in  the  armature-circuit. 

If  we  follow  the  diagram,  we  shall  see  that  when  the 
current  gets  from  the  carbon  of  the  batteries  or  from  one 
of  the  small  dynamos — if  that  be  used  to  furnish  the  sup- 
ply— it  divides  at  C,  part  of  it  going  through  wire  2, 
through  the  armature-coils  to  the  rheostat,  at  which  point 
it  can  not  go  farther  unless  the  switch-arm  be  moved  to 
one  of  the  contact-points.  From  the  rheostat  it  returns 
to  the  batteries.  This  shows  why  it  is  necessary  to  be 
careful  and  not  let  this  current  pass  when  you  do  not 
want  to  run  the  motor.  In  regular  work,  the  current 
should  be  turned  through  the  field  before  it  is  admitted 
to  the  armature. 

The  other  part  of  the  current  will  rush  through  the 
field-coil  as  soon  as  one  of  the  keys  is  pressed,  the  direc- 
tion of  this  part  depending  upon  which  key  is  used ;  but 


74 


STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 


in  either  case,  this  part  will  leave  the  reverser  at  Z  and 
return  to  the  batteries  through  wire  7. 

The  rheostat,  in  this  arrangement,  takes  the  part  of 
the  usual  "starting-box,"  which  allows  the  current  to 
enter  the  armature  through  resistance  until  it  gets  a 
speed  and  is  capable  of  protecting  itself  with  the  current 
it  makes  while  running. 

EXPERIMENT  56.  Motor  No.  1,  shunt-wound 
and  reversible,  with  a  second  method  of  speed  control. 

142.  Directions.  Fig.  54  shows  this  second  plan,  and 
it  will  be  noted  that  in  this  case  we  have  the  rheostat 


Fig-  54 

placed  in  the  field-shunt  and  that  we  also  reverse  the 
current  in  the  same  shunt.  The  armature-current  will 
be  one  that  we  must  look  out  for  so  as  not  to  short- 
circuit  it,  as  this  would  soon  weaken  the  batteries.  The 
one-point  switch,  K,  will  protect  the  batteries  if  it  be 
opened  as  soon  as  you  want  to  stop  the  motor. 

Try  the  effect  of  pressing  one  of  the  keys  of  the  re- 
verser, then  closing  switch  K,  and  finally  turning  the 
arm  of  the  rheostat  to  different  positions.  You  will  find 
that  you  can  reverse  the  motor  and  regulate  its  speed, 
hut  take  particular  notice  whether  it  runs  faster  with 
much  or  little  resistance  put  into  the  field-circuit. 

143.  Discussion.  If  the  proper  connections  be  made 
in  the  above  experiment,  the  student  will  find  that,  con- 
trary to  all  of  the  other  experiments,  the  motor  runs 


SPEED  REGULATION  AND  DIRECTION  OF  ROTATION        75 

slower  as  we  cut  out  resistance  in  the  field-shunt  by  turn- 
ing the  rheostat-arm  around  in  a  clockwise  direction,  as 
usual.  In  all  of  the  experiments  with  the  series-wound 
motor,  as  well  as  with  the  previous  shunt-wound  ar- 
rangement, the  less  the  resistance,  the  more  the  speed. 

We  still  have  some  troubles  to  overcome,  as  you  will 
see  by  the  wiring  that  lets  the  current  to  the  armature, 
for  it  is  evident  that  the  whole  force  of  the  current  is 
allowed  to  pass  into  the  armature  when  it  is  standing 
still.  This  will  not  make  any  trouble  in  the  little  experi- 
mental motors,  but  it  would  be  a  serious  thing  in  the 
motors  used  for  regular  work. 

144.  Direct-Current  Shunt-Wound  Motors.  We  have 
already  seen  what  is  meant  by  coils  in  "shunt,"  so,  when 
we  have  the  field-coil  and  the  armature-coils  arranged 
in  this  manner,  we  say  that  we  have  a  shunt-wound  ma- 
chine, whether  it  be  a  motor  or  a  dynamo. 

In  some  of  the  experiments  we  have  practical  wiring 
on  the  small  motors,  and  see  how  these  motors  are  regu- 
lated as  to  direction  of  rotation  and  speed. 

The  series-wound  motors,  as  explained  in  the  last  sec- 
tion, tend  to  "run  away"  when  the  load  is  removed,  and 
this  trouble  the  shunt-wound  motors  overcome ;  in  fact, 
a  well-made  shunt-wound  motor  will  run  at  almost  a  con- 
stant speed,  even  if  the  load  be  changed,  provided  it 
receives  a  direct  current  of  constant  voltage.  In  these 
motors,  the  resistance  of  the  armature-coils  is  small  in 
comparison  to  that  of  the  field ;  in  fact,  when  a  large 
shunt-wound  motor  is  started,  the  whole  force  of  the 
current  is  turned  through  the  field-coils  to  create  a  strong 
magnetic  field  before  any  is  allowed  to  enter  the  arma- 
ture.. This  is  all  accomplished  by  the  "starting-box,"  the 
connections  of  which  are  designed  to  do  this.  As  will 
be  explained  in  another  section,  it  is  veiy  important  to 


76  STUDY  OF  ELECTRIC  MOTORS  BY  EXPERIMENT 

have  the  armature  come  up  to  speed  gradually  to  give 
it  a  chance  to  generate  current  like  a  dynamo  to  hold 
the  regular  current  back.  If  it  were  not  for  this,  the 
armature  could  not  stand  the  heavy  current. 

Generally  speaking,  the  field  of  shunt-wound  motors  is- 
of  constant  strength,  no  matter  what  is  happening  to 
the  current  in  the  armature,  for  the  field-coils  are  con- 
nected to  the  mains  leading  the  current  to  the  motor.  In 
this  winding,  then,  we  do  not  have  the  counter-electro- 
motive force  in  the  armature  affected  to  any  great  ex- 
tent by  the  magnetic  flux  of  the  field. 

Now,  when  the  load  is  increased  on  a  shunt-wound 
motor  and  it  tends  to  slow  down,  thus  reducing  the 
counter-electromotive  force  in  the  armature,  in  rushes 
more  current  through  the  armature,  for  the  path  is  easier 
than  before.  This  increased  current  through  the  arma- 
ture brings  it  back  to  speed  at  once;  and  we  have  very 
little  effect  from  the  field,  as  this  has  remained  practically 
constant  in  strength.  Small  motors  are  not  quite  so  self- 
regulating  as  the  large  ones,  as  in  these  there  is  not  so 
much  difference  in  resistance  between  the  field  and  arma- 
ture. 

145.  Regulation  of  Field-Magnetism.  As  just  sug- 
gested, the  resistances  of  the  two  circuits  of  regular  shunt- 
wound  motors  are  very  different.  The  field-magnet  is 
wound  with  many  turns  of  wire,  thus  giving  it  enough 
resistance  to  allow  the  full  force  of  the  current,  for  a 
time,  without  too  much  heating;  at  least,  this  coil  will 
stand  this  current  until  the  armature  gets  under  way,  and 
then  the  whirling  of  the  armature  fans  the  field-coils  and 
tends  to  keep  them  cool. 

The  armature  has  a  small  resistance,  as  compared  with 
that  of  the  field-coils,  so  care  must  be  taken  to  keep  the 
full  force  of  the  current  from  entering  it  until  it  gets 


SPEED  REGULATION  AND  DIRECTION  OF  ROTATION        7/ 

almost  to  full  speed.  This  applies  to  large  motors,  of 
course,  the  small  ones,  say  up  to  and  including  one-sixth 
horse-power,  being  so  designed  that  they  may  be  started 
with  full  current. 

In  Experiment  55  we  regulated  the  speed  by  placing 
the  rheostat  in  the  armature-circuit,  but  this  wastes  much 
power.  As  the  armature-resistance  is  much  smaller  than 
that  of  the  field-coil,  the  armature  will  take  most  of  the 
current  and  we  shall  have  to  arrange  to  handle  all  of 
this  current  through  the  rheostat.  In  this  arrangement, 
the  rheostat  has  to  be  large  to  stand  the  heating  effects 
when  the  current  is  held  back,  and  so,  if  we  want  the 


Fig.  55 

motor  to  run  at  only  half  speed,  we  shall  have  to  waste 
a  great  deal  of  power  in  the  form  of  heat  that  is  lost  at 
the  rheostat: 

When  the  magnetism  of  the  field  is  regulated  to  con- 
trol the  speed,  we  have  but  a  small  part  of  the  whole 
current  to  handle  in  the  field-rheostat,  and  so  it  does  not 
make  so  much  difference  if  a  part  of  this  is  lost. 

EXPERIMENT  57.  Motor  No.  1,  shunt-wound  and 
reversible,  with  speed  control  by  regulation  of  field- 
magnetism,  together  with  starting-box. 

146.  Directions.  Fig.  55  shows  a  method,  for  experi- 
mental purposes,  of  letting  the  current  into  the  armature 
slowly.  The  connections  are  about  the  same  as  for  Ex- 
periment 56,  a  small  rheostat  being  placed  in  the  arma- 


/3  STUDY  OF  ELECTRIC  MOTORS  BY  EXPERIMENT 

ture-circuit,  as  shown.  The  one-point  switch,  K,  takes 
the  place  of  the  "main  switch"  on  regular  motors,  and 
this  should  be  opened  when  the  motor  is  to  be  stopped, 
to  make  sure  that  no  current  passes  through  the  arma- 
ture when  the  motor  is  not  running,  thus  wasting  the 
batteries. 

After  you  have  made  the  desired  connections,  see  that 
the  starting-box,  that  is,  the  rheostat  in  the  armature- 
circuit,  is  so  arranged  with  the  lever  at  the  right-hand 
side  that  no  current  can  pass  through  it,  and  that  the 
switch-arm  of  the  field-rheostat  is  placed  as  shown,  with 
all  resistance  cut  out.  Close  the  main  switch,  press  the 
left-hand  key  of  the  reverser,  then  turn  the  lever  of  the 
starting-box  to  the  left  upon  the  first  contact-point.  The 
motor  should  start  up  slowly  with  the  three-cell  battery, 
its  speed  gradually  increasing  as  the  resistance  is  cut  out 
by  turning  the  starting-box  lever  to  the  left.  To  get 
more  speed,  turn  the  arm  on  the  field-rheostat  to  the 
left  so  as  to  add  resistance  and  lessen  the  strength  of 
the  field-magnet. 

In  stopping  the  motor,  open  the  main  switch  first,  then 
bring  the  other  parts  to  the  original  starting-points. 

147.  Discussion.    We  have  here  a  very  good  example 
of  the  two  effects  of  resistance.     In  the  armature  we  get 
more  speed  by  cutting  out  resistance,  while  in  the  field- 
magnet  coils  we  add  resistance  to  get  more  speed.     This 
will  be  spoken  of  again  under  Section  151  on  "counter- 
electromotive  force." 

148.  Starting-Boxes.     If  we  wish  to  use  a  motor  for 
regular  work  and  do  not  care  to  reverse  it,  and  if  the 
motor  is  simply  to  run  at  a  certain  speed  for  which  it 
was  designed,  we  have  a  much  easier  thing  to  accomplish 
than  the  numerous  requirements   just  studied.     As  the 
shunt-wound  motor  is  the  one  generally  used  for  such 


SPEED  REGULATION  AND  DIRECTION  OF  ROTATION        79 

work,  it  will  only  be  necessary  to  explain  this  special 
motor  here. 

We  have  already  discussed  the  relative  resistances  in 
the  field-  and  armature-coils,  and  have  seen  the  necessity 
of  letting  the  current  into  the  armature  slowly,  thus  al- 
lowing it  to  come  up  to  speed  gradually.  This  can  all 
be  done  with  one  instrument,  called  a  starting-box,  a 
simple  plan  of  which  is  shown  in  Fig.  56.  In  this,  the 
parts  are  shown  in  the  position  taken  before  the  motor 
is  started,  the  switch-arm  resting  upon  a  dead-point.  If 


Fig.  56 

you  imagine  this  arm  turned  to  the  first  contact-point, 
you  will  see  that  the  current  can  pass  along  in  the  direc- 
tion shown  by  the  arrow  to  the  pivot  of  the  switch-arm 
and  then  through  the  arm  to  the  contact-point,  at  which 
place  it  divides,  part  of  it  going  through  an  electromag- 
net, M,  and  so  on  through  the  field  and  out  at  the  main 
switch.  The  other  part  goes  through  all  of  the  resist- 
ance-coils and  then  through  the  armature.  The  wires 
leading  to  the  armature  are  represented  as  being  large 
to  show  that  this  resistance  is  small  in  comparison  to 
that  of  the  field,  and  because  the  armature  takes  most  of 
the  current.  The  drawing  shows  that  the  motor  under 
consideration  is  a  plain  shunt-wound  motor. 

If  the  switch-arm  be  now  turned  to  the  second  and 
third  contact-points,  etc.,  resistance  will  be  cut  out  of  the 
armature-circuit,  thus  allowing  more  current  to  go 


8O  STUDY  OF  ELECTRIC  MOTORS  BY  EXPERIMENT 

through  the  armature,  as  it  increases  in  speed.  Here  is 
where  the  counter-electromotive  force  helps ;  for  the 
armature  generates  a  current  of  higher  and  higher  volt- 
age as  it  goes  faster  and  faster,  and  so  we  can  let  in 
more  and  more  current  and  still  not  burn  out  the  arma- 
ture, which,  we  have  seen,  has  very  little  resistance,  and 
which  would,  therefore,  take  too  much  current  if  it  were 
not  for  this  extra  resistance  to  be  overcome  as  it  gains 
in  speed. 

When  all  of  the  resistance  has  been  cut  out  of  the 
armature  and  it  is  getting  the  full  force  of  the  current 
like  the  field,  the  switch-arm  has  reached  a  point  at  which 
an  iron  plate  on  it  touches  the  poles  of  the  electromagnet, 
M,  where  it  will  be  attracted  so  long  as  the  current  flows 
and  the  motor  is  running.  The  arm  is  really  under  two 
pulls,  as  a  spring  is  trying  to  pull  it  away  from  the  mag- 
net. In  case  the  current  is  shut  off  at  the  central  sta- 
tion for  any  purpose,  the  motor  will  stop;  and  as  this 
magnet  can  no  longer  hold  the  switch-arm,  it  is  quickly 
pulled  back  to  the  starting-point  again.  This  "release- 
magnet"  is  a  splendid  thing,  as  it  keeps  the  full  current 
from  rushing  through  the  armature  when  they  turn  the 
current  on  again  at  the  central  station. 

By  this  simple  plan,  then,  the  field-magnet  is  energized 
first,  and  then  the  current  is  gradually  increased  in  the 
armature  as  the  speeM  increases.  The  coils  in  the  usual 
starting-box  are  not  large  enough  to  take  the  full  cur- 
rent for  any  length  of  time  without  too  much  heating,  as 
they  are  designed  to  carry  the  current  for  a  few  seconds 
only,  while  the  armature  is  getting  up  to  speed.  The 
spring  that  pulls  the  switch-arm  back  really  protects  the 
coils,  for  the  current  can  not  be  left  partly  on.  If  you  let 
go  of  the  switch-arm  before  it  reaches  the  release-magnet, 
the  arm  will  fly  back  again  and  open  the  circuit.  As  the 


SPEED  REGULATION  AND  DIRECTION  OF  ROTATION        8l 

magnet  lets  go  of  the  arm  as  soon  as  there  is  no  current 
in  the  line,  it  is  called  a  "no-voltage  release." 

EXPERIMENT  58.  Counter-electromotive  force  of 
motors. 

149.  Directions.  Arrange  a  three-cell  battery,  Motor 
No.  i,  a  key,  and  a  three  and  one-half  volt  electric  lamp, 
as  shown  in  Fig.  57.  As  will  be  seen  by  the  wiring,  the 
motor  is  series-wound  and  the  lamp  forms  a  shunt  to 
the  motor-circuit. 

Press  the  key  to  allow  the  current  to  start  the  motor 


St 


Fig.  57 

and  note  the  action  of  the  lamp.  When  the  motor  has 
its  full  speed,  gradually  stop  it  by  holding  the  armature- 
shaft,  watching  the  lamp. 

150.  Discussion.  We  have  in  this  arrangement  two 
paths  for  the  current  as  it  leaves  the  batteries  and  reaches 
the  lamp  at  L,  one  path  being  along  wire  2  through  the 
motor  and  back  to  the  batteries  through  wire  3.  The 
other  part  goes  through  the  lamp  and  then  through  wires 
4  and  3  to  the  batteries.  From  this  it  will  be  seen  that 
the  lamp  is  a  shunt  of  fairly  uniform  resistance,  if  we 
neglect  the  change  in  resistance  due  to  its  change  in  bril- 
liancy, and  that  the  motor  is  a  resistance  that  changes 
with  the  speed. 

When  the  motor  is  held  so  that  it  can  not  turn,  its  re- 
sistance is  merely  that  of  the  wires  in  its  coils,  and  as 
this  resistance  is  small,  the  motor  takes  most  of  the  cr-- 
rent,  leaving  very  little  for  the  lamp. 


82  STUDY  OF  ELECTRIC  MOTORS  BY  EXPERIMENT 

As  soon  as  the  motor  gains  speed,  it  generates  a  coun- 
ter-electromotive force  which  holds  back  the  battery  cur- 
rent, thus  adding  resistance  to  that  of  the  wires.  We 
know  from  previous  experiments  that  when  we  increase 
the  resistance  of  one  shunt,  the  other  shunt  has  to  carry 
more  current,  and  this  is  made  clear  by  the  lamp,  which 
brightens  as  the  motor  goes  faster  and  faster. 

151.  Counter-Electromotive  Force.  The  last  experi- 
ment showed  that  a  motor  has  a  much  greater  resistance 
when  running  than  when  still.  The  armature-resistance 
is  the  one  that  is  affected  by  the  increasing  speed,  and 
that  is  why  it  is  necessary  to  put  a  starting-box  in  the 
armature-circuit  of  shunt-wound  motors.  The  field  can 
take  care  of  itself  on  account  of  its  high  resistance,  but 
the  armature  would  burn  out  at  once  on  large  motors  if 
the  whole  current  were  allowed  to  pass  through  its  coils 
of  small  resistance.  As  mentioned,  when  speaking  of  the 
starting-box,  the  little  coils  of  resistance-wire  hold  the 
full  force  of  the  current  back  until  the  speed  is  such  as 
to  create  the  counter-electromotive  force.  This  repre- 
sents a  current  flowing  in  the  opposite  direction  to  that 
which  makes  the  motor  go. 

We  have  already  mentioned  the  fact  that  motors  will 
generate  a  current  if  rapidly  turned  by  a  steam-engine 
or  by  some  other  power  as,  for  example,  water-power. 
In  the  case  of  the  motor  just  used,  the  motor  was  run  by 
the  electrical  energy  supplied  by  the  batteries ;  that  is, 
the  batteries  represent  the  engine.  If  we  look  at  it  in 
this  way  we  can  easily  see  that  the  motor  should  gen- 
erate a  current,  even  if  run  by  electricity.  In  "The  Study 
of  Dynamos  by  Experiment"  we  shall  see  what  gener- 
ates this  current. 

If  a  motor  be  well  made,  it  will  generate  a  current 
having  a  voltage  that  is  nearly  as  high  as  that  of  the 


SPEED  REGULATION  AND  DIRECTION  OF  ROTATION        83 

current  which  enters  the  armature  and  runs  it.  This 
shows  that  the  armature  gets  very  little  current  from  the 
supply,  when  it  is  running  at  full  speed,  compared  with 
what  it  would  get  if  the  armature  stood  still. 

From  this  we  see  that,  in  order  to  make  the  motor 
go,  the  current  that  enters  it  from  the  supply  must  be 
of  a  greater  voltage  than  that  of  the  counter-electromotive 
force.  There  is  a  constant  struggle  between  the  applied 
electromotive  force  and  the  counter-electromotive  force, 
and  it  is  just  this  struggle  in  overcoming  the  counter- 
electromotive  force  which  changes  the  electrical  energy 
supplied  to  the  motor  to  the  mechanical  energy  which 


Fig.  58 

the  motor  has  as  it  turns.  If  it  were  not  for  this  forcing 
back  of  the  counter-current,  the  motor  would  not  go  any 
more  than  a  water-wheel  would  turn  without  the  pres- 
sure of  the  water  against  the  resisting  buckets. 

EXPERIMENT  59.  To  show  in  which  direction 
the  counter-current  flows  in  a  motor. 

152.  Directions.  In  Fig.  58  we  have  Motor  No.  i,  a 
key,  and  a  current  detector  arranged  so  that  the  detector 
will  be  a  shunt  of  the  motor.  Place  the  motor  about 
three  feet  from  the  detector  so  that  its  magnetic  needle 
will  not  be  affected  by  the  electromagnets  of  the  motor. 
The  motor  may  be  at  one  end  of  the  table,  away  from 
the  other  apparatus. 

Press  the  key  for  a  moment,  at  the  same  time  noting 
in  which  direction  the  north  pole  of  the  compass-needle 


84  STUDY  OF  ELECTRIC  MOTORS  BY  EXPERIMENT 

turns  when  wire  5  touches  the  key,  K.  If  arranged  as 
in  the  figure,  current  will  enter  the  detector  through 
wire  4,  shown  by  the  full-line  arrow,  causing  a  certain 
deflection  of  the  north  pole,  and  as  this  detector-shunt  is 
of  low  resistance,  the  motor  will  not  turn  rapidly.  Now 
disconnect  wire  5,  press  the  key  to  allow  the  motor  to 
get  a  high  speed,  raise  the  key  to  disconnect  the  batter- 
ies, and  quickly  touch  wire  5  to  wire  3  or  to  the  contact 
on  the  key  that  is  attached  to  wire  3.  Note  that  the 
detector-needle  is  deflected  in  the  same  direction  as  be- 
fore. 

153.  Discussion.    From  the  second  part  of  the  experi- 
ment we  see  that,  as  the  needle  is  deflected  in  the  same 


Fig.  59 


way  as  before,  the  current  must  enter  the  detector  from 
wire  4  again.  It  is  evident  that  when  the  current  came 
from  the  batteries,  it  followed  the  direction  through 
wire  2  shown  by  the  full-line  arrow,  and  that  when  the 
counter-current  came  from  the  motor  to  deflect  the  needle, 
it  must  have  passed  through  wire  2  in  the  direction 
shown  by  the  dotted  arrow.  This  shows  that  the  coun- 
ter-electromotive force  pushes  against  the  applied  cur- 
rent, as  discussed  in  some  of  the  other  sections.  This 
experiment  must  be  done  quickly  and  before  the  motor 
has  slowed  down  much. 

EXPERIMENT  60.  Regulation  of  speed  with 
lamps  in  parallel. 

154.  Directions.  Arrange  six  three  and  one-half  volt 
lamps  in  parallel,  as  shown  in  Fig.  59,  placing  the  "bank 


SPEED  REGULATION  AND  DIRECTION  OF  ROTATION        85 

of  lamps"  in  series  with  Motor  No.  i,  a  three-cell  bat- 
tery and  a  key.  Try  the  effect  on  the  speed  of  the  motor 
of  turning  on  more  or  less  lamps. 

155.  Discussion.  As  these  lamps  are  so  joined  that 
each  can  let  some  current  through  from  wire  I  to  wire  2, 
it  is  evident  that,  when  several  lamps  are  screwed 
in,  more  current  will  pass  than  when  one  or  two  are 
used.  If  the  cells  are  strong,  two  lamps  will  run  the 
motor  slowly,  and  it  will  be  seen  that  these  light  up 
brighter  than  when  more  are  used.  The  faster  the  motor 
runs,  the  greater  the  counter-electromotive  force  and  the 
less  each  lamp  has  to  carry. 


CHAPTER  IX 

VARIOUS  ELECTRIC  MOTORS 

156.  Small  Motors  and  Large  Motors  are  names  that 
do  not  mean  as  much  as  they  seem  to  at  first,  when  we 
consider  that  a  small  motor  may  be  so  wound  as  to  take 
a  large  current,  and,  in  the  same  way,  a  large  motor 
may  be  so  arranged  as  to  need  a  current  of  small  voltage. 

A  more  useful  classification  would  be  to  put  the  motors 
that  are  to  be  run  with  batteries  and  other  small  currents 
together  and  call  them  low-voltage  motors,  then  the  ones 
that  are  to  be  run  from  the  no-  or  ii5-volt  currents 
would  be  called  high-voltage  motors.  This  point  of  classi- 
fication does  not  amount  to  much,  although  it  might  prove 
to  be  a  serious  thing  to  try  to  run  a  low-voltage  motor 
upon  a  high-voltage  circuit ;  that  is,  it  might  be  serious 
for  the  motor.  Chapter  10  will  give  information  upon 
this  part  of  the  subject. 

All  that  need  be  said  here  is  that  motors  intended  for 
use  with  battery  currents  and  currents  from  low-voltage 
dynamos  are  so  wired  that  their  resistance  is  low.  High- 
resistance  motors  would  hold  the  current  from  a  few  bat- 
teries back  to  such  an  extent  that  there  would  not  be 
enough  electromagnetism  produced  to  turn  the  armature. 
We  can,  by  proper  apparatus  (see  Chap.  10),  run  low- 
voltage  motors  upon  high-voltage  currents;  but,  if  we 
were  to  do  this  without  modifying  the  current,  we  should 
ruin  the  motor  by  burning  out  its  coils  and  doing  other 
damage. 

157.  Compound-Wound  Motors.     In  discussing  the 
series-wound  machine,  we  saw  that  the  coils  of  the  field 

86 


VARIOUS    ELECTRIC    MOTORS 


and  armature  were  in  series,  and  that  in  the  shunt-wound 
machine  the  coils  are  in  parallel,  each  taking  a  part  of 
the  current. 

In  the  compound-wound  motor  we  have  a  cross  be- 
tween these  two  methods,  as  the  field  is  provided  with  a 
series-coil  and  a  shunt-coil.  Fig.  60  gives  an  idea  as  to 
how  this  is  arranged,  and  how  the  starting-box  is  placed 
in  the  circuits  to  allow  the  motor  to  start  up  slowly  so 
as  not  to  burn  out  the  armature. 

The  two  coils  on  the  field  are  wound  so  that  the  cur- 
rent which  flows  through  them  magnetizes  the  field  in  the 
same  direction;  that  is,  so  that  both  coils  aid  each  other 


SWRT1H6-BOX. 

..-  1 

SH 

r*  ,T    .1 

/vvv 

Fig.  60 

in  making  a  north  pole  at  the  same  pole-piece.  We 
have  in  this  winding  the  best  part  of  both  the  series  and 
shunt  machines,  for  by  this  combination  we  get,  in  a 
degree,  the  powerful  starting-torque  of  the  series  ma- 
chine and  the  steady  speed  of  the  shunt-wound  motor. 

158.  Comparison  of  Series,  Shunt  and  Compound 
Motors.  Compound-wound  motors  start  more  promptly 
than  shunt-wound  motors,  and  they  will  stand  overloads 
better  than  the  shunt-wound  machines.  Under  changes 
of  load  the  compound-wound  motors  will  vary  in  speed 
more  than  the  shunt  motors,  but  they  will  not  vary  nearly 
so  much  as  the  series  motors.  Compound- wound  motors 
are  advised  for  the  small  sizes  that  are  to  be  started  with- 
out starting-boxes. 


88  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

The  speed  of  series-wound  motors  varies  greatly  with 
the  load,  and  when  the  load  is  entirely  thrown  off,  they 
will  race  unless  proper  resistance  be  thrown  into  the  cir- 
cuit. 

Shunt-wound  motors  are  more  or  less  self-regulating, 
the  large  sizes  being  able  to  run  at  almost  constant  speed, 
no  matter  whether  the  load  be  large  or  small,  provided 
the  load  is  within  the  capacity  of  the  machine.  The 
smaller  sizes  of  this  variety  are  not  so  self-regulating  as 
the  large  ones,  and  so  their  speed  will  vary  slightly  with 
the  load.  They  will  not  race,  for,  as  soon  as  the  speed 
begins  to  increase,  the  increasing  counter-electromotive 
force  will  decrease  the  current  supplied  to  the  armature, 
and  this  keeps  the  speed  within  limits. 

159.  Differentially- Wound  Motors.     This  is  similar 
to  the  compound- wound  motor,  as  just  described,  except 
in  the  arrangement  of  the  two  coils  that  are  placed  on 
the  field.    In  this  case  we  have  a  series-coil  and  a  shunt- 
coil,  but  the  two  are  so  wound  that  they  work  against 
each  other.     By  this  plan  the  strength  of  the  field  is 
due  to  the  difference  in  the  magnetizing  effects  of  the 
two  coils,  hence  the  name,  differential. 

A  motor  of  this  winding  will  run  at  a  very  constant 
speed,  but  the  shunt-wound  motor  will  give  a  speed  that 
is  constant  enough,  and,  besides,  there  are  some  draw- 
backs to  the  differential  winding  in  case  the  motor  is 
overloaded.  The  student  will  not  meet  this  winding  un- 
der ordinary  circumstances. 

160.  Alternating-Current  Motors  are  made  in  many 
ways,  and  as  the  average  student  will  not  have  a  chance 
to  take  up  this  part  of  the  subject  experimentally,  this 
branch  of  the  work  will  be  omitted.     The  subject  of  al- 
ternating currents  is  a  large  one ;  in  fact,  it  is  too  large 
to  be  considered  in  this  small  book  of  experiments. 


VARIOUS    ELECTRIC    MOTORS  89 

161.  Railway  Motors.     We  have  already  mentioned 
the  series-wound  motors  as  being  adapted  for  use  on 
electric  cars  on  account  of  the  powerful  starting-torque. 
When  a  loaded  car  is  started,  the  power  needed  to  get  it 
under  way  is   many   times  that  needed   to   keep   it   in 
motion  when  once  started,  especially  if  the  car  is  stopped 
on  a  grade.     These  motors  are  easily  regulated  as  to 
speed  and  load,  and  so  the  direct-current  series-wound 
motors  are  most  commonly  used  for  this  purpose.     Con- 
trollers are  used  for  starting  and  regulating  the  speed, 
and  these  may  be  so  arranged  that  the  two  motors  on 
the  car  can  be  joined  in  series  or  in  parallel,  with  or  with- 
out resistance. 

Motors  used  for  this  class  of  work  are  made  in  special 
ways  for  special  purposes  and  have  to  be  very  strong  and 
well  protected  to  stand  the  constant  pounding  and  abuse 
given  them. 

162.  Special  Motors.    Electric  motors  are  used  for  so 
many  things  nowadays  that  it  would  take  a  very  large 
book  to  mention  even  a  small  part  of  the  various  appli- 
cations of  these  wonderful  machines.     The  shapes  and 
sizes  have  been  ingeniously  adapted  to  the  numerous  re- 
quirements, and  we  find  motors  working  silently  in  all 
kinds  of  places  and  for  all  kinds  of  power.    Large  manu- 
facturers of  motors  will  design  special  motors  for  special 
purposes  and  arrange  their  various  parts  to  do  the  work 
required. 

163.  Protection  of  Motors.     As  an  electric  motor  is 
a  machine,  at  least  as  much  care  should  be  given  to  it  as 
to  any  machine ;  in  fact,  even  more  care  should  be  given 
to  electric  motors  than  is  given  to  most  machines,  as 
they  are  very  apt  to  be  abused  with  overloads.    A  well- 
made  motor  runs  so  quietly  and  makes  so  little  fuss  in 
doing  its  work  that  we  are  liable  to  get  the  idea  that  it 

\ 


-90  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

has  no  limit  to  its  powers  and  that  it  can  do  no  end  of 
work.  This  is  a  great  mistake,  and  so  all  motors  to  be 
used  on  regular  commercial  circuits  should  be  well  pro- 
tected with  fuses  or  other  safety  devices.  As  has  been 
stated  in  the  various  discussions,  a  motor  takes  more  cur- 
rent as  its  load  is  increased  and  its  speed  decreased;  so 
it  must  be  evident  that,  if  the  load  be  increased  suffi- 
ciently, the  motor  will  turn  very  slowly,  or  even  stop. 
As  soon  as  the  counter-electromotive  force  decreases,  the 
resistance  of  the  armature  is  so  small  that  we  get  more 
current  through  it  than  it  can  carry ;  and  so  the  wires 
would  be  melted  if  they  were  not  protected.  This  pro- 
tection is  given  by  using  fuses  in  the  circuit  that  will 
melt  at  some  stated  number  of  amperes,  or  by  other  au- 
tomatic devices  that  will  open  the  circuit  before  the  cur- 
rent gets  near  the  danger  point. 

Motors  larger  than  one-sixth  horse-power  should  be 
protected  with  a  starting-box  having  a  "no-voltage  re- 
lease" (see  Sec.  148). 

164.  Motor  No.  2.  While  Motor  No.  2  is  similar  in 
construction  to  Motor  No.  i,  it  is  larger  and  stronger 
than  No.  I,  and  it  is  furnished  in  either  of  two  windings. 
It  may  be  had  as  a  plain  series-wound  motor,  as  showrn  in 
Fig.  61,  this  style  being  listed  as  No.  2205,  the  price  being 
$2.00.  In  order  to  do  the  experimental  work  that  can  be 
done  with  Motor  No.  i,  however,  it  has  to  be  provided 
with  four  binding-posts  and  some  changes  have  to  be 
made  in  the  wiring  in  order  that  it  may  be  run  as  either 
a  series-wound  or  a  shunt-wound  motor.  This  motor, 
with  the  changes  made  for  experimental  work,  is  listed 
as  No.  2206  and  costs  $2.25.  In  either  winding  the  bind- 
ing-posts for  the  field  are  mounted  upon  the  wooden  base, 
and  the  brushes  are  adjustable  while  running  at  full 
speed.  This  feature  is  valuable,  as  it  is  necessary  to  get 


VARIOUS    ELECTRIC    MOTORS  91 

the  proper  pressure  of  the  brushes  upon  the  commutator 
for  best  results. 

Motor  No.  2  stands  four  and  one-half  inches  high.  It 
is  finished  in  black  enamel  with  nickeled  trimmings,  and 
the  field-magnets  are  strong,  plenty  of  iron  being  used  in 
their  construction. 

165.  Dynamo-Motor  No.  3.  This  machine  is  also  fur- 
nished to  students  in  two  styles  of  winding  in  order  to 
adapt  it  exactly  to  the  requirements.  Fig.  62  shows  the 
dynamo-motor  as  plain  shunt-wound,  this  style  being  ad- 
vised when  it  is  to  be  used  as  a  plain  motor  or  dynamo, 


Fig.  61  Fig.  62 

no  changes  being  needed  in  direction  of  rotation.  This 
winding  is  listed  as  No.  2209,  and  it  is  shown  in  Fig.  62. 
Price,  $3.75. 

When  it  is  necessary  to  change  the  direction  of  rotation 
as,  for  example,  in  running  certain  toys,  this  dynamo- 
motor  may  be  purchased  with  an  extra  attachment  which 
gives  the  machine  four  binding-posts.  In  this  form  it  may 
be  connected  to  the  rheostat,  current  reverser,  etc.,  ex- 
plained in  connection  with  Motor  No.  i.  With  the  extra 
binding-posts  and  other  attachments  not  found  upon  any 
other  small  dynamos,  this  machine  is  especially  adapted 


92  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

for  experimental  and  general  purposes.  It  can  be  used 
as  a  series-wound  or  shunt-wound  motor  and  as  a  shunt- 
wound  dynamo,  and  is  listed  as  No.  2210.  Price,  $4.00. 

As  a  motor,  it  will  run  with  the  current  from  batteries 
or  with  the  current  generated  by  a  twin  machine  turned 
by  some  power.  Two  No.  3  dynamo-motors  make  a  com- 
plete electrical  power  plant  if  you  have  some  method  of 
turning  the  dynamo,  which  will  generate  current  for  the 
other  machine  to  run  as  a  motor.  Motors  No.  i  and 
Xo.  2  run  well  on  the  current  from  one  of  these  ma- 
chines ;  in  fact,  you  can  furnish  current  for  all  kinds  of 
experimental  work,  including  bells,  telephone  lines,  in- 
duction-coils, plating  outfits,  miniature  lighting  outfits, 
electric  cars,  charging  storage  batteries,  etc. 

The  construction  of  this  machine  is  mechanical.  The 
field  is  cast  solid,  the  coils  being  form-wound  and  con- 
nected in  multiple.  The  armature  is  of  the  drum  type, 
one  and  three-fourths  inches  in  diameter,  built  up  of 
punchings;  that  is,  it  is  laminated,  with  six  slots.  The 
brushes  are  adjustable.  The  pulley,  one  inch  in  diameter, 
is  grooved  for  a  small  round  belt.  Oil  cups,  black  enamel 
finish.  When  run  at  3,000  r.p.m.,  gives  good  current 
Safe  maximum  load,  6  volts  4  amperes.  If  run  as  a 
power  motor,  from  4  to  6  volts  give  the  best  results. 
The  very  best  way  to  run  this  as  a  dynamo  is  to  use  a 
one-eighth  horse-power  motor  in  connection  with  the 
bank  of  lamps  explained  in  Section  180. 

166.  110-Volt  Motors,  as  has  been  explained,  are 
properly  wound  to  take  the  commercial  current,  and  they 
develop  a  counter-electromotive  force  sufficient  to  protect 
the  armature  when  it  gets  up  to  speed.  For  the  small 
sizes  up  to  and  including  the  one-sixth  horse-power  a 
starting-box  is  not  generally  used  except  for  special  rea- 
sons. Small  motors,  if  well  made,  will  start  off  very 


VARIOUS    ELECTRIC    MOTORS    •  93 

quickly  without  endangering-  the  coils  unless  the  load  be 
excessive.  A  few  sizes  are  illustrated  to  give  the  student 
an  idea  as  to  their  construction  and  appearance. 

All  motors  heat  up  when  they  are  running  under  a 
load,  but  of  course  the  heat  must  not  get  too  great.  The 
small  motors  shown  in  the  following  cuts  are  of  the 
standard  ventilated  protected  type,  and  are  guaranteed 
to  carry  their  full  rated  load  continuously  without  attain- 
ing a  temperature  greater  than  40  degrees  Cent,  in  ex- 
cess of  that  of  the  surrounding  air  in  all  parts  except 
commutator,  and  45  degrees  Cent,  on  the  commutator. 

Machines  up  to  i  horse-power  will  carry  25  per  cent 
overload  for  one  hour  with  temperature  rise  not  to  exceed 
55  degrees  Cent,  for  all  parts  except  commutator,  and 
60  degrees  Cent,  on  the  commutator.  Machines  of  I 
horse-power  and  above  will  carry  25  per  cent  overload 
for  two  hours  with  rise  of  55  degrees  Cent,  for  all  parts 
except  commutator,  and  60  degrees  Cent,  on  the  com- 
mutator. Machines  are  not  guaranteed  to  carry  continu- 
ous overloads.  All  types  of  these  machines  will  carry  50 
per  cent  overload  momentarily  without  injury.  These 
ratings  are  based  on  condition  that  the  motors  are  so 
placed  as  to  receive  free  circulation  of  air. 

For  use  in  places  where  they  require  protection  from 
dust  and  dirt,  chips,  flying  particles,  or  protection  from 
mechanical  injury,  motors  may  be  furnished  with  either 
brass  wire  gauze  or  solid  iron  enclosures,  and  as  all 
motors  generate  heat  w-hile  running,  and  as  this  heat  is 
not  radiated  as  rapidly  in  closed  as  in  open  motors,  the 
ratings  for  enclosed  motors  are  somewhat  lower  than  for 
open  motors. 

167.  Motors  for  Intermittent  Duty.  For  many  classes 
of  service,  such  as  the  running  of  elevators  and  hoists, 
motors  have  such  intermittent  duty  that  there  is  little  or 


94  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

no  trouble  from  the  accumulation  of  heat,  the  load-limit 
in  these  cases  being  reached  when  sparking  at  the  brushes 
becomes  serious.  Motors  for  strictly  intermittent  service 
are  therefore  rated  higher  than  for  constant  service. 

168.  110- Volt  Laboratory  Motors.     If  you  have  the 
i  lo-volt  current  in  your  laboratory,  you  will  find  that 
a  small  motor  will  be  of  the  greatest  help  in  running  small 
dynamos  and  other  things.     The  sizes,  from  one-eighth 
horse-power  to  and  including  one-quarter  horse-power, 
will  be  as  large  as  are  usually  found  for  experimental 
purposes.     A  one-eighth  horse-power   motor  will   do   a 
great  deal,  and  even  run  light  machinery,  such  as  jig- 
saws and  other  small  things. 

If  these  motors  are  run  in  connection  with  a  bank  of 
lamps,  as  explained  in  Section  180,  the  speed  will  be 
under  perfect  control  and  there  will  be  no  danger  of 
burning  out  any  fuses  in  the  house  even  if  you  happen 
to  get  a  short  circuit  while  experimenting. 

The  following  descriptions  of  motors  are  taken  from 
the  manufacturer's  catalogues,  and  they  are  herein  re- 
produced for  the  guidance  of  those  who  are  interested  in 
the  matter.  Such  descriptions  are  instructive,  for  they 
explain  the  special  points  of  each  motor  illustrated.  The 
author  does  not  wish  the  term  "laboratory  motors"  to  be 
misleading.  He  has  chosen  the  name  simply  because 
these  motors  are  so  useful  and  so  well  adapted  for  labora- 
tory purposes.  The  motors  described  below  are  all  com- 
mercial motors  intended  for  hard  work,  and  they  are 
suggested  because  the  author  is  familiar  with  them,  hav- 
ing personally  used  all  of  the  illustrated  sizes  for  various 
purposes.  Compound  windings  are  advised  for  these 
small  motors. 

169.  A   One-Eighth  Horse-Power  Motor.     For  the 
amateur  and  student  a  motor  of  this  size  will  be  large 


VARIOUS    ELECTRIC    MOTORS  95. 

enough  to  do  most  of  the  work  needed.  It  will  run 
the  small  dynamos  that  are  shown,  run  jig-saws  and 
other  light  machinery.  Fig.  63  shows  a  one-eighth  horse- 
power motor,  called  "Frame  40,"  that  is  well  suited  for 
laboratory  work,  as  it  will  stand  constant  hard  usage. 
It  is  of  handsome  and  artistic  outline,  and,  while  being 
well  ventilated,  it  is  perfectly  protected  and  satisfies  the 
requirements  of  a  motor  having  no  external  current- 
carrying  parts.  It  is  especially  adapted  for  use  in  posi- 
tions where  the  motor  is  in  easy  reach  of  the  operator,  as 
it  avoids  the  possibility  of  touching  moving  or  electrified 


Fig.  63 

parts.  The  author  has  used  a  number  of  these  motors 
and  has  found  them  very  satisfactory.  The  latest  design 
of  the  one-eighth  horse-power  motors  differs  slightly 
from  that  shown  in  the  cut,  an  improvement  having  been 
made  in  the  brush-holder.  These  motors  run  at  2,000 
'revolutions  per  minute  (2,000  r.p.m.)  with  full  load.  A 
motor  of  this  size  weighs  about  16  pounds  and  is  pro- 
vided with  a  2-inch  grooved  pulley. 

170.  A  One-Seventh  Horse-Power  Motor.  Fig.  64 
shows  this  size,  and  although  there  does  not  seem  to  be 
much  difference  between  the  fractions  y$  and  1-7,  this 
motor  will  meet  more  severe  conditions  of  service  than 


96  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

the  one  just  described.  The  frame  of  this  motor  is  about 
the  same  size  as  that  for  the  one-eighth  motor,  but  it  is 
heavier  and  more  solid,  mechanically,  stands  more  over- 
load, and  can  be  wound  for  higher  speeds  than  the  for- 
mer. Weight,  18  pounds ;  runs  at  2,000  r.p.m. 

To  illustrate  what  can  be  done  in  changing  these 
motors,  using  the  same  frame,  this  motor  can  be  so 
wound  that  it  will  give  one-sixth  horse-power  at  2,300 
r.p.m.  This  speed  is  rather  high,  however,  for  laboratory 


Fig.  64 

purposes,  but  it  illustrates  how  the  speed  and  power  can 
be  varied  at  will  by  changing  the  wiring  of  a  motor. 

171.  Another  One-Seventh  Horse-Power  Motor  that 
is  very  useful  and  efficient  is  shown  in  Fig.  65.  This  is 
styled  "Frame  i/7-P,"  and  it  was  designed  specially  for 
driving  automatic-playing  musical  instruments.  Its  prin- 
cipal qualities,  which  especially  fit  it  for  this  class  of 
service,  are  extreme  durability,  noiselessness,  cleanliness, 
ability  to  run  for  long  periods  locked  up  in  the  instrument 
case  without  attention,  powerful  starting-torque,  small 
dimensions  in  the  direction  where  space  is  usually  limited 
— i.e.,  over  the  shaft  and  pulley — and  the  general  conve- 
nience and  ease  of  its  installation.  These  qualities  have 


VARIOUS   ELECTRIC    MOTORS  97 

been  found  valuable  in  many  other  kinds  of  service,  and 
although  designed  for  a  piano  motor,  it  is  finding  ex- 
tended sale  outside  of  the  musical  instrument  trade.  The 
frame  No.  1/7- P  is  furnished  either  with  or  without  en- 
closing covers,  the  enclosure  being  recommended  only 
where  necessary  for  the  protection  of  the  working  parts 
of  the  motor,  as  the  motors  will  run  cooler  without  the 


Fig.  65 

cover,  especially  under  heavy  loads.  Whether  with  or 
without  covers,  the  motors  are  ventilated  by  perforations 
in  the  lower  halves  of  the  heads.  This  frame  will  be 
furnished  with  sliding  base  when  ordered.  This  feature 
is  often  very  valuable  in  a  motor  desired  for  driving 
automatic-playing  musical  instruments,  as  it  allows  the 
belt  to  be  kept  at  the  proper  tension  without  the  neces- 
sity of  cutting  and  resplicing  it.  Sliding  bases  can  not 
be  furnished  with  any  other  of  the  small  motor  frames. 


98  STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

172.  A  One-Quarter  Horse-Power  Motor.  Fig.  66 
shows  a  very  practical  design  for  a  motor  of  this  power, 
and  although  the  illustration  is  about  the  same  size  as 
that  for  the  other  motors  shown,  the  motor  itself  is  much 
larger  and  heavier  than  the  others.  This  is  of  the  ven- 
tilated protected  type  with  bi-polar  frame,  and  these  are 
generally  shunt-wound  with  flat  pulley,  as  shown.  Each 


Fig.  66 

motor  is  furnished  with  sliding  base  with  belt-tightening 
attachment  and  with  a  starting-box  having  a  no-voltage 
release. 

A  motor  of  this  rating  is,  really,  a  powerful  motor,  and 
it  will  do  a  great  deal  of  work.  The  author  has  used  them 
for  running  very  large  static  machines,  like  those  used 
by  doctors  for  medical  purposes,  and  with  a  proper  rheo- 
stat, the  speed  is  under  perfect  control.  A  motor  of  this 
size  will  run  quite  a  little  light  machinery. 

173.  A  One-Tenth  Horse-Power  Motor.  This  is  an- 
other small  motor  that  should  be  added  to  the  above  list 
to  make  it  complete  and  to  show  another  kind  of  con- 
struction. This  is  shown  in  Fig.  67  and  can  be  made  to 
run  on  alternating  current  as  well  as  upon  direct  current. 


VARIOUS    ELECTRIC    MOTORS  99 

This  is  a  practical  small  motor  costing  a  little  less  than 
the  one-eighth,  but  of  course  it  is  not  so  powerful  as  the 
one-eighth,  which,  however,  will  not  run  on  the  alter- 
nating current.  When  furnished  for  running  on  alter- 
nating current,  the  field-cores  are  laminated.  When  sup- 
plied for  direct  current,  the  field-cores  are  cast  solid. 

The  winding  can  be  arranged  to  give  one-thirtieth,  one- 
twentieth,  one-sixteenth  or  one-tenth  horse-power,  ac- 
cording to  the  speed  required.  The  relative  speeds  for 


Fig.  67 

these  powers  are  1,000,  1,500,  2,000  and  3,000  r.p.m. 
These  motors  are  furnished  with  three  grooved  pulleys, 
their  diameters  being  three-quarters,  nine-sixteenths  and 
seven-sixteenths  inches,  and  the  motor  weighs  four  and 
one-half  pounds. 

One  point  the  student  must  consider  when  thinking  of 
such  a  motor  is  that  it  is  series-wound,  thus  adapting  it 
for  a  fairly  uniform  load.  These  small  motors  are  made 
to  run  for  long  periods  without  attention  and  are  just 
the  thing  when  adapted  to  the  work  they  have  to  do.  For 
laboratory  work  they  are  not  so  good  as  the  one-eighth, 
which  are  compound-wound,  but  where  alternating  cur- 
rent is  supplied  they  can  be  used  instead  of  the  other 
forms  described  above. 

It  should  be  stated,  however,  that  while  this  little  motor 


IOO        STUDY  OF  ELECTRIC   MOTORS  BY  EXPERIMENT 

will  run  well  on  either  direct  or  alternating  current  where 
but  little  power  is  required,  it  is  not  strong  enough  to 
properly  run  Dynamo-Motor  No.  3  up  to  speed  for  gen- 
erating a  good  current.  If  the  student  has  only  alterna- 
ting current  in  his  laboratory  and  wants  to  run  one  of 
these  dynamo-motors,  he  will  need  a  one-eighth  horse- 
power alternating-current  motor.  The  author  can  recom- 
mend Motor  No.  2254  for  this  purpose. 


CHAPTER  X 
ELECTRIC  CURRENT  FOR  RUNNING  MOTORS 

174.  Various  Methods.     The  current  needed  to  run 
your  motors  will  be  determined  by  the  particular  motors 
you  have,  for  the  current  should  be  of  the  proper  voltage 
required  to  get  the  best  results. 

The  current-supply  for  laboratory  purposes  will  be 
either  from  batteries  or  from  dynamos.  In  the  latter 
case,  the  dynamos  may  be  in  the  room  and  under  control 
of  the  student  or  they  may  be  at  the  power-house  where 
the  commercial  current  is  generated.  The  following  sec- 
tions will  give  suggestions  as  to  the  various  methods  that 
may  be  used  to  run  the  motors  described  in  this  book. 

175.  Battery  Currents  are  sufficient  for  all  of  the  ex- 
periments given,  and  where  it  is  not  possible  to  generate 
your  own  current  or  get  it  from  the  street,  this  will  be 
the  plan  to  adopt.    There  are  many  kinds  of  batteries  on 
the  market,  some  being  adapted  for  long  runs  and  others 
being  sufficient  where  short  runs  for  experimental  work 
only  are  required.     For  the  usual  work  required  in  the 
laboratory,  ordinary  dry  batteries  of  good  quality  do  very 
nicely.     They  are  comparatively  cheap  and  there  are  no 
dangers  from  acids  or  fumes ;  besides,  they  can  be  readily 
replaced  when  they  get  too  weak. 

176.  Forcing  Dry  Batteries  is  a  very  poor  plan,  as 
it  shortens  their  life  very  rapidly.    A  dry  battery  is  really 
intended  for  intermittent  work,  and  if  run  too  long  at  a 
time  or  forced  too  hard,  it  will  not  give  the  best  re- 
sults.    The  best  plan  is  to  use  two  or  three  times  as 

101 


IO2         STUDY  OF  ELECTRIC   MOTORS  BY   EXPERIMENT 

many  cells  as  are  needed  to  get  the  desired  voltage,  ar- 
ranging them  as  suggested  below  to  increase  the  amperes. 

177.  Arrangement  of  Cells.  Fig.  68  shows  three  cells 
arranged  in  series,  this  combination  giving  about  four 
and  one-half  volts.  This  three-cell  set  will  light  small 
lamps  and  run  Motor  No.  i  at  a  high  rate  of  speed,  and 
should  be  used  when  combined  with  the  eleven-point 
rheostat  and  other  things  mentioned  in  the  experiments. 

Fig.  69  shows  two  sets  of  three  cells  each,  the  two 
being  joined  in  multiple;  that  is,  the  whole  is  arranged 
in  "multiple  series."  By  this  plan  the  voltage  of  the 

c— ^ 


Fig.  68  Fig.  69 

combined  cells  remains  the  same  as  that  of  the  three 
cells,  while  the  amperes  are  doubled  in  quantity.  In 
other  words,  by  this  plan  we  have  more  quantity  to  draw 
upon  at  the  same  pressure  as  before,  so  each  cell  does 
not  get  the  work  that  it  otherwise  would. 

If  you  wish  to  run  your  motors  for  any  length  of 
time  for  fans  or  other  purposes,  it  will  pay  you  to  arrange 
the  batteries  as  shown ;  for,  by  this  plan,  you  will  be  able 
to  get  much  more  out  of  them  before  they  give  out. 

178.  Storage-Batteries  are  very  satisfactory  for  run- 
ning motors  and  for  other  laboratory  purposes,  especially 
if  you  have  means  of  charging  them  yourself.  This  can 


ELECTRIC   CURRENT  FOR  RUNNING   MOTORS  103 

be  done  very  easily  if  you  have  the  no-volt  direct  current, 
using  a  bank  of  lamps.  Even  if  you  do  not  have  a  com- 
plete bank  of  lamps,  as  explained  in  Section  180,  you  can 
get  the  proper  attachments  at  small  expense  for  this  work. 

For  running  induction-coils  and  other  things  that  need 
a  strong  current,  good  storage  batteries  are  fine ;  for  they 
give  results  that  dry  batteries  can  not  duplicate.  Storage 
batteries  can  be  bought  for  $1.00,  $2.00,  etc.,  per  cell,  ac- 
cording to  size. 

179.  Running  Small  Motors  from  Small  Dynamos. 
If  you  have  a  dynamo  that  will  generate  the  right  cur- 


Fig.  70 


rent  for  your  small  motors  and  some  way  of  turning  the 
dynamo,  you  have  a  complete  electric  plant.  There  are 
several  methods  of  operating  the  dynamo:  by  hand- 
power,  by  means  of  a  steam-  or  a  gas-engine,  by  water- 
power,  by  an  electric  motor,  etc.  For  those  who  have 
water-power,  this  is  a  very  satisfactory  method,  although 
it  would  not  pay  to  arrange  a  water-power  plant  for  run- 
ning one  of  the  small  dynamos  like  the  No.  3  described 
above.  At  his  country  laboratory  the  author  has  a  fine 
water-power  running  a  3-k.w.  dynamo  which  furnishes 
current  for  all  lighting  and  experimental  work,  and  so 
the  matter  of  running  small  dynamos  is  a  very  simple 
one,  as  it  is  in  the  city  where  the  commercial  no-volt 
current  is  to  be  had. 


1O4        STUDY  OF  ELECTRIC   MOTORS  BY   EXPERIMENT 

Fig.  70  shows  a  handy  form  of  hand-power  for  running 
the  Dynamo-Motor  No.  3  (Sec.  165).  This  will  do 
for  short  runs  for  experimental  purposes. 

The  best  way  for  those  who  have  the  no- volt  direct 
current  is  to  run  a  one-eighth  horse-power  motor  through 
a  bank  of  lamps  to  regulate  the  speed,  and  then  belt  the 
dynamo  to  this.  By  this  plan,  as  has  been  mentioned,  the 
dynamo  can  be  made  to  deliver  all  voltages  within  its 
capacity,  as  the  speed  is  so  easily  controlled. 

Fig.  71  shows  such  a  plan,  the  current  from  the  small 


dynamo  being  passed  to  switches  or  to  a  switch-board. 
This  matter  of  switch-boards  and  handling  the  current 
from  the  dynamos  for  small  plants  will  be  taken  up  in 
"The  Study  of  Dynamos  by  Experiment." 

180.  Bank  of  Lamps.  This  is  a  very  useful  piece  of 
laboratory  apparatus,  especially  as  it  adds  greatly  to  the 
safety  of  things.  In  all  experimental  work,  one  is  apt 
to  make  short  circuits  by  accident,  and  this  causes  trouble 
by  blowing  out  the  fuses  in  the  house.  The  only  thing 
that  happens  when  a  short  circuit  is  made  in  the  circuit 
leading  from  the  lamps,  if  arranged  as  in  Fig.  71,  is  that 
the  lights  will  come  up  to  full  candle-power.  By  putting 
a  fuse-plug  in  place  of  one  of  the  lamps,  of  course,  the 
full  current  will  be  passed  through  the  bank  of  lamps 
and  then  the  fuses  will  blow  if  a  short  circuit  be  made. 


ELECTRIC   CURRENT  FOR  RUNNING   MOTORS  IO5 

One  should  be  very  careful  to  think  out  what  will  take 
place  in  the  circuit  before  closing  any  switches  on  no- 
volt  currents. 

These  lamps  should  be  thoroughly  insulated  and  care- 
fully arranged,  and  if  they  are  to  be  used  in  the  city,  they 
should  be  on  a  slate  base  to  comply  with  the  regulations 
of  the  National  Board  of  Fire  Underwriters.  For  a  six- 
lamp  bank,  the  slate  base  should  be  from  20  inches  to  2 
feet  long,  8  or  9  inches  wide  and  about  I  inch  thick. 
Holes  must  be  drilled  and  plugged  with  lead  tubing  to 
hold  the  screws  for  the  various  parts.  The  author  has 
made  a  number  of  these  for  general  purposes  with  six 
lamps,  mounting  them  on  slate  painted  dead  black,  and 
he  finds  them  very  useful  for  regulating  the  speed  of 
no-volt  motors  that  are  used  for  running  jig-saws,  small 
dynamos,  and  other  light  machinery. 

In  charging  storage  batteries,  and,  in  fact,  for  regu- 
lating the  current,  there  is  nothing  better.  By  using  as- 
sorted lamps  of  8,  16  and  32  candle-power,  a  very  fine 
adjustment  can  be  made.  Each  16  c.p.  lamp,  screwed  in, 
allows  one-half  an  ampere  of  current  to  pass  through  the 
apparatus.  The  8  c.p.  lamp  passes  one-quarter  ampere, 
and  a  32  c.p.  one  ampere.  (  By  proper  combinations, 
you  can  get  just  what  you  need.  Such  an  outfit,  with 
flexible  cords,  fuses,  switch,  receptacles,  etc.,  mounted 
upon  a  slate  base,  costs  about  $5.00,  not  including  the 
lamps.  It  can  be  attached  to  any  socket. 

181.  Battery  Regulator  for  110-Volt  Currents.  Fig. 
72  shows  a  method  of  regulating  the  no-volt  current  so 
that  it  can  be  used  for  running  small  motors,  etc.,  with- 
out danger  and  without  too  much  sparking.  The  author 
has  used  lead  plates  in  sulphuric  acid  for  this  purpose, 
but  they  are  decidedly  unpleasant  to  handle,  to  say  noth- 
ing of  the  troubles  that  come  if  they  tip  over.  The 


106        STUDY  OF  ELECTRIC  MOTORS  BY  EXPERIMENT 

method  now  employed  and  the  cleanest  method,  is  to  use 
dry  batteries,  the  number  depending  upon  the  work  to 
be  done.  These  can  be  joined  in  multiple  so  as  to  get 
the  desired  number  of  amperes.  As  will  be  seen  by  re- 
ferring to  Fig.  72,  the  current  passes  from  the  bank  of 
lamps  through  the  batteries  and  back — the  wires  leading 
to  your  apparatus  being  connected  to  the  batteries,  as 
shown ;  that  is,  the  current  you  use  is  merely  a  shunt  of 
the  high-voltage  current. 

The  batteries  should  be  properly  joined  to  the  com- 
mercial current;  that  is,  they  should  be  considered  as 


Fig.  72 

storage  batteries  that  are  being  charged.  Test  the  wires 
leading  from  the  bank  of  lamps  by  putting  them  in  a 
tumbler  of  water  into  which  you  have  dissolved  a  little 
ordinary  salt.  The  negative  wire  will  give  off  large  quan- 
tities of  hydrogen  bubbles.  Tie  a  knot  in  this  wire  to 
mark  it,  connect  this  to  the  zinc  end  of  the  battery  regu- 
lator and  the  other  wire  to  the  carbon  end ;  that  is,  place 
negative  to  negative  and  positive  to  positive,  as  in  the 
case  of  charging  storage  batteries. 

With  proper  switches  so  that  you  can  vary  the  num- 
ber of  batteries  and  by  using  more  or  less  lamps  on  your 
bank  of  lamps,  you  can  get  all  of  the  variations  in  cur- 
rent that  will  be  needed. 


Condensed  Price-List  of 
Apparatus  Described  in  This  Book 

NOTE — We  cannot  accept  orders  for  less  than  $oc. 


List 
No. 

Name  of  Article 

Set 
Sec- 
tion 

See 
Fig. 

Price 

Postage 
Extra 

1341 
1319 
1351 
1312 
1505 
1501 
1502 
1083 
1084 
1085 
1728 
1062 
1724 
1725 
1415 
1451 
1452 
1312 
2201 
2205 
2206 
2209 
2210 
2212 
2253 
2254 
2175 

1101 
1102 
1103 

Steel  Needles  (Pkg.  of  25)  ... 
Horseshoe  Magnet  (English)  . 
Iron  Filings  in  box  

$0.03 
.12 
.02 
.18 
.20 
.10 
.15 
.06 
.15 
.20 
.25 
.05 
.25 
.35 
.35 
.20 
.02 
.18 
1.00 
2.00 
2.25 
3.75 
4.00 
3.75 
11.70 
25.00 

5.00 
.12 
.25 
.35 

$0.01 

.03 
.01 
.05 
.02 
.02 
.03 
.02 
.03 
.03 
.03 
.02 
.04 
.05 
.08 
.04 
.02 
.05 
.15 
.38 
.38 
6*6  Ibs. 
6y2  Ibs. 
21      Ibs. 
20     Ibs. 
25     Ibs. 

.06 
.10 
.15 

Round  Bar  Magnet 

Pocket  Compass  (Brass)  

17 
18 
8 
9 
10 
11 
13 
15 
16 
26 

Simple  Current  Detector  
Handy  Current  Detector  
Strap  Key  

60 
61 

50 
51 
52 
53 
55 
57 
58 
75 

Strap  Key  
Strap  Key  with  side  switch... 
Double-Key  Current  Reverser. 
Two-Point  Switch  . 

Five-Point  Rheostat  
Eleven-Point  Rheostat  
Experimental  Electromagnets. 

Soft  Iron  Core  for  No.  1451... 

Motor  No.  1,  complete  
Motor  No.  2  series,  wound... 
Motor  No.  2  series  or  shunt.. 
Dynamo-Motor  No.  3  
Dynamo-Motor  No.  3  
Hand-Power  for  No.  2210  
One-Eighth  H.P.  Motor  (D.C.). 
One-Eighth  H.P.  Motor  (A.C.). 
Bank  of  Lamps  (slate  base,  no 

106 
164 
164 
165 
165 
179 
169 

180 

39 
61 
61 
62 

70 
63 

72 

St.  J.  Dry  Battery,  small  
Improved  Two-Cell  Battery.. 
Improved  Three-Cell  Battery. 

Fun  With  Magnetism  and  Fun  With  Electricity  have  started  more  young 
men  upon  electrical  careers  than  any  other  scientific  outfits  ever  placed  be- 
fore the  public.  The  thousands  upon  thousands  that  have  been  sold  in  all 
parts  of  the  world  have  furnished  fun  and  science  for  people  of  all  ages, 
and  the  mere  fact  that  they  are  listed  by  the  New  York  Board  of  Educa- 
tion, and  recommend  to  the  pupils  and  teachers  of  the  New  York  public 
and  private  schools  is  a  guarantee  of  their  value.  Were  it  not  for  the 
fact  that  these  are  made  in  such  large  quantities  and  sold  by  stores,  agents 
and  mail-order  houses,  the  price  would  De  much  higher.  Don't  fail  to  get 
these.  They  have  a  national  reputation. 

FUN  WITH  MAGNETISM 

This  outfit  contains  a  32-page  book  of  instructions,  with  45  illustrations, 
together  with  a  complete  set  of  apparatus  for  performing  61  fascinating 
experiments.  It  will  give  you  some  new  ideas  about  magnetism  and  start 
you  at  the  right  place  in  your  study  of  electricity.  Think  what  that  means — 
to  start  right  1 

The  book  contajns  experiments  with  the  horseshoe  magnet,  with  bar 
magnets,  with  floating  magnets,  etc.,  etc.,  thus  giving  a  practical  knowledge 
of  the  subject;  and  it  is  all  done  in  such  an  interesting  way  that  one  can't 
help  remembering  it.  Every  experiment  clinches  some  fact  and  every  fact 
is  important. 

Amusing  Experiments. — Something  for  Nervous  People  to  Try. — The 
Jersey  Mosquito. — The  Stampede. — The  Runaway. — The  Dog-fight. — The 
Whirligig. — The  Naval  Battle. — A  String  of  Fish. — A  Magnetic  Gun. — A 
Top  Upsidedown. — A  Magnetic  Windmill. — A  Compass  Upsidedown. — The 
Magnetic  Acrobat. — The  Busy  Ant-hill. — The  Magnetic  Bridge. — The  Merry- 
go- Round. — The  Tight-rope  Walker. — A  Magnetic  Motor  Using  Attractions 
and  Repulsions. — And  43  Others. 

No.  Rl. — Complete  outfit  "Fun  with  Magnetism" $0.25 

If  sent  by  mail,  postage  extra 05 


FUN  WITH  ELECTRICITY 

The  author  of  this  Fun  with  Science  series  has  spent  a  great  deal  of 
time  and  money  in  experimenting  to  devise  apparatus  that  will  do  the 
proper  work  and  be,  at  the  same  time,  simple  and  cheap,  and  in  no  outfit 
has  he  succeeded  better  than  in  Fun  with  Electricity.  When  you  think 
of  an  outfit  retailing  for  50c.  and  covering  the  whole  subject  of  "Static 
Electricity,"  giving  60  scientific  experiments  upon  its  production,  conduc- 
tion and  induction,  with  a  55-page  book  of  instructions  with  38  drawings, 
and  a  complete  set  of  apparatus  of  20  articles  for  performing  these  60  ex- 
periments, you  will  understand  why  the  sales  of  this  outfit  have  been 
enormous.  As  the  subject  is  presented  in  a  fascinating  way — and  not  as 
mere  dry  science-^-every  one  likes  to  do  the  experiments.  No  wonder  these 
sets  are  highly  praised  by  parents  and  educators  in  every  part  of  the  country! 

There  is  Fun  in  these  Experiments:  Chain  Lightning. — An  Electric 
Whirligig. — The  Baby  Thunderstorm. — A  Race  with  Electricity. — An  Elec- 
tric Frog  Pond. — An  Electric  Ding-Dong. — The  Magic  Finger. — Daddy 
Long-Legs. — Jumping  Sally. — An  Electric  Kite. — Very  Shocking. — Con- 
densed Lightning. — An  Electric  Fly-Trap. — The  Merry  Pendulum. — An 
Electric  Ferry-Boat.— A  Funny  Piece  of  Paper. — A  Joke  on  the  Family 
Cat. — Electricity  Plays  Leap-Frog. — Lightning  Goes  Ov  r  a  Bridge.— Elec- 
tricity Carries  a  Lantern. — And  40  Others. 

There  isn't  an  outfit  anywhere  at  any  price  that  gives  better  value  for  the 
money.  An  ideal  present  for  a  boy. 

No.  R2.— Complete  outfit  "Fun  with  Electricity" $0.50 

If  sent  by  mail,  postage  extra 1; 


FUN  WITH  PUZZLES 

Here  is  an  outfit  that  every  boy  and  girl  should  have,  for  it  is  amusing, 
instructive  and  educational.  It  is  real  fun  to  do  puzzles  and  to  puzzle  your 
friends,  and  this  book  contains  some  real  brain-teasers  that  will  make  you 
think.  The  book  contains  15  chapters,  80  pages,  and  128  illustrations,  and 
measures  5x7 1/2  inches.  If  you  can't  do  any  particular  puzzle  you  will 
find  its  solution  in  the  "key,  which  is  bound  with  the  book.  If  you  want 
to  win  prizes  by  doing  the  puzzles  in  the  magazines,  you  will  find  this  book 
of  four  hundred  puzzles  a  regular  school  of  puzzles  that  will  give  you  a 
thorough  training  for  this  kind  of  work.  The  book  alone  is  well  worth 
the  price,  to  say  nothing  of  the  outfit  of  numbers,  counters,  pictures,  etc. 

Contents  of  Book:  Chapter  (1)  Secret  Writing.  (2)  Magic  Triangles, 
Squares,  Rectangles,  Hexagons,  Crosses,  Circles,  etc.  (3)  Dropped  Letter 
and  Dropped  Word  Puzzles.  (4)  Mixed  Proverbs,  Prose  and  Rhyme.  (5) 
Word  Diamonds,  Squares,  Triangles,  and  Rhomboids.  (6)  Numerical  Enig- 
mas. (7)  Jumbled  Writing  and  Magic  Proverbs.  (8)  Dissected  Puzzles. 
(9)  Hidden  and  Concealed  Words.  (10)  Divided  Cakes,  Pies,  Gardens, 
Farms,  etc.  (11)  Bicycle  and  Boat  Puzzles.  (12)  Various  Word  and 
Letter  Puzzles.  (13)  Puzzles  with  Counters.  (14)  Combination  Puzzles. 
(IS)  Mazes  and  Labyrinths. 

Secret  Writing  is  explained  in  this  book,  and  it  shows  how  you  can  write 
letters  to  your  friends  and  be  sure  that  no  one  can  read  them  unless  they 
are  also  in  the  secret.  This  one  thing  alone  will  give  you  a  great  deal  of 
enjoyment.  Get  this  outfit  and  have  some  fun. 

No.  R3. — Complete  outfit  "Fun  with  Puzzles" $0.25 

If  sent  by  mail,  postage  extra OS 


FUN  WITH  SOAP-BUBBLES 


Fancy  Bubbles  and  Films  are  not  easily  blown 
and   even  with  the   proper   outfit   one   must   "kno 


without  special  apparatus, 
ow   how."     That's  why  we 

furnish  a  16-page  book  with  every  set  to  show  just  how  to  do  it.  With  the 
aid  of  the  21  illustrations  and  the  directions  you  can  produce  remarkable 
results  that  will  surprise  and  entertain  your 
friends.  A  child  can  do  it  as  well  as  a  grown 
person. 

Soap-Bubble  Parties  using  these  outfits  create 
real  sensations.  Why  not  be  the  first  in  your  town 
to  give  a  "Fun  with  Soap-Bubbles  Party?"  Just 
write  and  ask  about  the  price  for  any  special  num- 
ber of  them  —  say  six  or  a  dozen. 

Contents  of  Book:  Twenty-one  Illustrations.  — 
Introduction.  —  The  Colors  of  Soap-Bubbles.  —  The 
Outfit.—  Soap  Mixture.—  Useful  Hints.—  Bubbles 
Blown  with  Pipes.  —  Bubbles  Blown  with  Straws.  —  Bubbles  Blown  witl 
the  Horn.  —  Floating  Bubbles.  —  Baby  Bubbles.  —  Smoke  Bubbles.—  Bombshell 
Bubbles.  —  Dancing  Bubbles.  —  Bubble  Games.  —  Supported  Bubbles.  —  Bubble 
Cluster.  —  Suspended  Bubbles.  —  Bubble  Lamp  Chimney.  —  Bubble  Lenses. 

—  Bubble  Basket.  —  Bubble  Bellows.  —  To  Draw  a  Bubble  Through  a  Ring.  — 
Bubble  Acorn.—  Bubble  Bottle.—  A  Bubble  Within  a  Bubble.—  Another  Way. 
—Bubble     Shade.—  Bubble     Hammock.—  Wrestling     Bubbles.—  A     Smoking 
Bubble.  —  Soap     Films.  —  The    Tennis     Racket     Film.  —  Fish-net     Film.  —  Pan- 
shaped  Film.  —  Bow  and  A.TOW  Film.  —  Bubble  Dome.  —  Double  Bubble  Dome. 

—  Pyramid    Bubbles.  —  Turtle-back    Bubbles.  —  Soap-Bubbles     and     Frictional 
Electricity. 


There   is   nothing  more   beautiful    than    the   airy-fairy    soap-bubble    with 
nging  colors."     This  outfit  gives  the  best  possible  amusement  for 


old  and  young. 

No.  R4. — Complete  outfit  "Fun  with  Soap-Bubbles" $0.25 

If  sent  by  mail,  postage  extra 07 

Three  extra  packages  of  Prepared  Soap,  post  paid 10 


FUN  WITH  SHADOWS 


What 

ter- 


No wonder  shadow-making  has  been  popular  for  several  centuries!  W 
could  give  keener  delight  than  comical  shadow-pictures,  pantomimes,  en 
tainments,  etc.?  Professional  shadowists  use  wires,  forms,  and  vari 
devices  to  aid  them,  and  that  is  why  they  get  such  wonderful  results  on 
the  stage.  Do  you  want  to  do  the  same  thing  right  in  your  own  home  and 
entertain  your  friends  with  all  kinds  of  fancy  shadows?  You  can  do  it 


with  this  outfit,  for  the  book  contains  100  illustrations  and  diagrams  with 

directions  for  using  the  numer- 
ous   articles    included     in     the 
box.     You  will  be  surprised  to 
see   how   easily   you   can   make 
these  funny  shadows  with   the 
aid   of   the   outfit.      Better    get 
one    now    and    make    shadows 
like  a  professional. 
The  Outfit  contains  everything  necessary  for  all  ordinary  shadow  pictures, 
shadow  entertainments,   shadow   plays,   etc.      The   following  articles  are   in- 
cluded:    One  book  of  Instructions  called  "Fun  with   Shadows";   1   Shadow 
Screen;  2  Sheets  of  Tracing  Paper;  1  Coil  of  Wire  for  Movable  Figures;   1 
Cardboard    Frame    for    Circular    Screen;     1    Cardboard    House    for    Stage 
Scenery;  1  Jointed  Wire  Fish-pole  and  Line;  2  Bent  Wire  Scenery  Holders; 
4  Clamps  for  Screen;   1   Wire  Figure  Support;    1   Wire  for  Oar;   2   Spring 
Wire  Table  Clamps;    1   Wire  Candlestick  Holder;   5   Cardboard   Plates  con- 
taining  the   following  printed  figures  that   should  be   cut   out   with   shears; 
12  Character  Hats;  1  Boat;  1  Oar-blade;  1  Fish;  1  Candlestick;  1  Cardboard 
Plate  containing  printed  parts  for  making  movable  figures. 

No.  R5.  —  Complete  outfit  "Fun  with  Shadows"  ...................   $0.25 

If  sent  by  mail,   postage  extra  ..........................  07 


FUN  WITH  PHOTOGRAPHY 

Popular  Pastimes  are  numerous,  but  to  many  there  is  nothing  more 
fascinating  than  photography.  The  magic  of  sunshine,  the  wonders  of 
nature,  and  the  beauties  of  art  are  tools  in  the_  hands  of  the  amateur 
photographer.  If  you  want  to  get  a  start  in  this  up-to-date  hobby,  this 
outfit  will  help  you.  You  will  enjoy  the  work  and  be  delighted  with  the 
beautiful  pictures  you  can  make. 

The  Outfit  contains  everything  necessary  for  making  prints — together 
with  other  articles  to  be  used  in  va- 
rious ways.  The  following  things  are 
included:  One  Illustrated  Book  of  In- 
structions, called  "Fun  With  Photog- 
raphy"; 1  Package  of  Sensitized 
Paper;  1  Printing  Frame,  including 
Glass,  Back,  and  Spring;  1  Set  of 
Masks  for  Printing  Frame;  1  Set  of 
Patterns  for  Fancy  Shapes;  1  Book 
of  Negatives  (Patented)  Ready  for 

Use;   6  Sheets  of  Blank  Negative   Paper;  1   Alphabet  Sheet;   1    Package  of 
Card  Mounts;   1  Package  of  Folding  Mounts;  1   Package  of  "Fixo." 

Contents  of  Book:  Chapter  I.  Introduction. — Photography. — Magic 
Sunshine. — The  Outfit. — II.  General  Instructions. — The  Sensitized  Paper. — 
How  the  Effects  are  Produced. — Negatives. — Prints. — Printing  Frames. — Our 
Printing  Frame. — Putting  Negatives  in  Printing  Frame. — Printing. — De- 
veloping.— Fixing. — Drying. — Trimming. — Fancy  Shapes. — Mounting.  —  III. 
Negatives  and  How  to  Make  Them. — The  Paper. — Making  Transparent 
Paper. — Making  the  Negatives. — Printed  Negatives. — Perforated  Negatives. 
— Negatives  Made  from  Magazine  Pictures. — Ground  Glass  Negatives. — 
IV.  Nature  Photography. — Aids  to  Nature  Study. — Ferns  and  Leaves. — 
Photographing  Leaves. — Perforating  Leaves. — Drying  Leaves,  Ferns,  etc., 
for  Negatives. — Flowers. — V.  Miscellaneous  Photographs. — Magnetic  Pho- 
tographs.— Combination  Pictures. — Initial  Pictures. — Name  Plates. — Christ- 
mas, Easter  and  Birthday  Cards. 

No.  R6. — Complete  outfit  "Fun  with  Photography" $0.50 

If  sent  by  mail,  postage  extra 10 


FUN  WITH  CHEMISTRY 

Chemistry  is  universally  considered  to  be  an  interesting  subject,  even  in 
school,  and  it  is  certainly  an  important  one  in  these  days  of  scientific 
progress.  This  outfit  starts  you  at  the  right  place  and  presents  the  elements 
of  the  subject  in  a  most  interesting  fashion.  The  experiments  are  so  en- 
joyable that  Vou  will  take  pleasure  in  doing  them  over  and  over  again,  and 
you  will  want  to  do  them  for  your  friends.  You  can  have  a  lot  of  fun 


Fun  With 

Chemistry. 


with  this  set,  and  even  if  you  have  taken  ad 
vanced  courses  in  the  subject  you  will  find 
something  new  in  these  experiments.  The 
more  you  know  about  chemistry  the  more 
you  will  enjoy  it,  for  then  you  can  more 
easily  appreciate  what  a  splendid  outfit  this 
is  for  the  money. 

The  Outfit  contains  over  20  different  arti- 
cles, including  chemicals,  test-tubes,  adjusta- 
ble ring-stand,  litmus  paper,  filter  paper, 
glass  tubing,  etc.;  in  fact,  everything  needed 
for  the  forty-one  experiments.  The  Book 
of  Instructions  is  fully  illustrated,  and  measures  5x7  J4  inches. 

Fun  Found  Here:  From  White  to  Black,  or  the  Phantom  Ship. — Yellow 
Tears. — Smoke  Pearls. — An  Ocean  of  Smoke. — A  Tiny  Whirlwind. — A 
Smoke  Cascade. — An  Explosion  in  a  Teacup. — A  Gas  Factory  in  a  Test- 
Tube — Making  Charcoal. — Flame  Goes  Over  a  Bridge. — A  Smoke  Toboggan- 
Slide.— Fountains  of  Flame.— Making  an  Acid.— Making  an  Alkali.— A 
Chemical  Fight.— Through  Walls  of  Flame.— An  Artificial  Gas  Well.— A 
Lampblack  Factory. — Steam,  from  a  Flame. — The  Flame  that  Committed 
Suicide.— Chemical  Soup.— A  Baby  Skating-Rink.— A  Magic  Milk-Shake.— 
The  Wizard's  Breath.— A  Chemical  Curtain.— Scrambled  Chemicals.— And 
Many  Other  Experiments. 

No.  R7. — Complete  outfit  "Fun  with  Chemistry" $0.50 

If  sent  by  mail,  postage  extra 10 


ELECTRIC  SHOOTING  GAME 

Shooting  Animals  by  electricity  is  certainly  a  most  original  game,  and  it 
will  furnish  a  vast  amount  of  amusement  to  all.  The  game  is  patented  and 
copyrighted — because  it  is  really  a  brand-new  idea  in  games — and  it  brings 
into  use  that  most  mysterious  something  called  electricity.  While  the 
electricity  is  perfectly  harmless,  there  being  no  batteries,  acids  or  liquids, 
it  is  very  active  and  you  will  have  plenty  to  laugh  at.  It  is  so  simple  that 
the  smallest  child  can  play  it  and  so  fasci-  .  _ 
nating  that  grandpa  will  want  to  try  it. 

The  "game-preserve"  is  neatly  printed  in 
colors,  and  the  birds  and  wild  animals  are 
well  worth  hunting.  Each  has  a  fixed  value 
— and  some  of  them  must  not  be  shot  at  all 
— so  there  is  ample  chance  for  skill.  Tissue- 
paper  bullets  are  actually  shot  from  the 
"electric  gun"  by  electricity,  and  it  is  truly 
a  weird  sight  to  see  them  shoot  through  the 
air  impelled  by  this  unseen  force. 

The  Outfit  contains  the  "Game-Preserve,"  the  "Electric  Gun,"  the  "Shoot- 
ing-Box," and  the  "Electric  Bullets,"  together  with  complete  illustrated 
directions,  all  placed  in  a  neat  box. 

No.   R41. — Complete  "Electric  Shooting  Game,"  postpaid $0.50 


NEW  IDEA  TIT-TAT-TOE 

Splendid  game  for  two,  three,  or  four  players;  great  improvement  upon 
the  good  old  game;  fascinating  game  instantly  learned;  nothing  better  for 
children's  parties  and  progressive  birthday  parties;  box  with  game-board, 
12  men,  directions;  discount  for  party  orders. 

No.  R21 — New  Idea  Tit-Tat-Toe,  sample,  postpaid   $0.15 


Fun  With  Telegraphy 

TWO  OUTFITS   FOR  AMATEURS  AND  STUDENTS 


Every  boy  can  make  use  of  telegraphy  in  one  way  or  another,  and  the  time 
•taken  to  learn  it  will  be  well  spent — to  say  nothing  about  the  fun.  After 
making  and  experimenting  with  about  one  hundred  models,  many  of  which 
were  good,  Mr.  St.  John  has  at  last  perfected  these  outfits,  which  he  can  per- 
sonally recommend.  They  are  so  practical  and  original  that  they  are  now 
being  made  in  large  quantities — hence  the  low  price. 

The  two  outfits  have  the  same  general  construction,  although  they  differ 
in  details,  each  being  designed  for  its  special  work.  The  "  keys,"  "  sounders" 
and  "binding-posts"  are  neatly  mounted  upon  ebonized  bases  with  nickel- 
plated  trimmings.  No  expensive  gravity  batteries  are  needed,  for  the  sound- 
ers are  designed  to  work  with  dry  batteries,  which  are  clean,  cheap,  and  per- 
fectly safe.  These  outfits  simplify  the  whole  subject  of  amateur  telegraphy 
and  make  it  a  pleasure. 

•"FUN  WITH  TELEGRAPHY "  is  designed  for  local  use  as  an  ideal 
"  Learners'  Outfit "  of  one  instrument.  Two  may  be  used  from  room  to  room, 
but  "  No.  2  "  is  better  for  regular  line  work. 

Outfit :  Illustrated  Book  of  Instructions,  called  "  Fun  with  Telegraphy  " ; 
Telegraph  " Key ";  Telegraph  "Sounder";   Spring  "Binding-posts";  Insu- 
Jated  Wires  for  connections. 
Price,  post-paid,  5O  cts ;   with  dry  cell,  post-paid,  65  eta. 

"  TELEGRAPHY  NO.  2  "  is  designed  for  regular  line  work.  The  stations 
may  be  several  hundred  feet  apart,  as  the  instruments  are  very  sensitive  in 
operation.  By  means  of  an  ingenious  switch,  either  station  may  "  call "  the 
other  at  any  time,  even  though  the  line  is  kept  on  "open  circuit."  There  is 
absolutely  no  waste  of  current  when  the  line  is  not  in  use,  and  this  is  certainly 
a  great  advantage  over  the  old  fashioned  methods  which  boys  have  heretofore 
been  obliged  to  use. 

Outfit:  Illustrated  Book  of  Instructions,  called  "Telegraphy  Number 
Two";  Telegraph  "  Key  ";  Telegraph  "Sounder,"  with  high-resistance  mag- 
aet,  and  an  adjustable  up-stop;  Special  "  Switch  "  for  controlling  the  batteries; 
Nickel-plated  Screw  "  Binding-posts";  Insulated  Wires  for  connections. 

Price,  post-paid,  75  cents;  with  two  dry  cells,  $1.OO 

THOMAS  M.  ST.  JOHN,  848  Ninth  Ave.,  New  York 


St.  J.  SEMI-WIRELESS 

[PATENT  APPLIED  FOR] 
A  SYSTEM  THAT  TELEGRAPHS  AND  TELEPHONES 

To  avoid  all  misunderstandings  we  wish  to  state  right  here  in  the  first 
sentence  that  by  the  name  "Semi-Wireless"  we  do  not  mean  "wireless," 
for  one  tiny  wire  must  join  all  of  the  stations  on  any  line,  and  two  wires  are 
still  better  than  one. 

Semi-Wireless  is  a  new  system  that  solves  the  telegraphic  problem  for 
amateurs  and  students.  It  is  simpler  and  cheaper  than  the  old-fashioned 
way,  with  its  slow-moving  telegraph  sounders  and  relays,  its  heavy  line- 
wire  and  its  mess  of  bluestone  batteries;  it  is  simpler,  cheaper  and  more 
reliable  than  wireless  with  its  coils  and  condensers,  its  tuning-coils  and 
transformers.  In  short,  it  is  the  ideal  system  no  matter  whether  there 
are  to  be  two  or  a  dozen  stations  on  the  line;  for  every  station  can  telegraph 
and  telephone  to  every  other  station.  Think  what  it  means  to  have  these 
two  great  things  combined  in  one  simple  system! 

In  wireless  work  a  great  deal 
of  energy  is  wasted, — because  it 
has  to  radiate  in  all  directions  in 
order  to  radiate  at  all, — and  so 
the  receiving-station  gets  only  the 
smallest  part  of  that  energy. 
Semi- Wireless  does  not  waste 
energy;  it  directs  it,  and  so  the 
messages  simply  have  to  go 
where  they  are  wanted,  right 
into  every  ear  on  the  line;  and 
that  is  why  so  little  power  gives 
such  remarkable  results.  One 
dry  battery  will  do  wonders  in 
telegraphing  over  a  ten-mile 
Semi- Wireless  line.  The  reason? 
No  waste  of  energy;  no  horse- 
power needed  to  get  a  flea-power 
to  the  right  spot;  no  dynamo 
wanted  to  get  a  dry-battery  ef- 
fect. Everything  is  economized, 
ether-waves  are  directed,  power 
is  concentrated  and  results  are 
absolutely  certain.  No  matter 
what  other  systems  you  have, 
you  need  a  Semi- Wireless. 

Semi-Wireless  is  a  brand-new 
system  that  satisfies,  for  it  tele- 
graphs and  telephones;  it  is  the 
best  thing  ever  invented  for 
students  of  telegraphy  and  wire- 
less, and  it  is  best  for  hard  service  over  long  lines.  We  guarantee  that 
Semi-Wireless  will  do  every  thing  we  say  it  will. 

The  instruments  are  strong  and  well  made,  and  when  once  set  up  all 
expense  ceases,  an  occasional  dry  battery  being  all  that  will  be  needed  to 
keep  it  going.  The  "directing  wire"  can  be  strung  up  in  a  little  while  by 
the  method  fully  explained  in  the  book  on  telegraphy  which  is  given  with 
each  instrument.  This  illustrated  book  gives  full  details  for  building  and 
operating  Semi-Wireless  lines,  and  it  also  includes  codes  and  numerous 
aids  to  learning  telegraphy. 

The  Standard  Instrument,  No.  2550,  is  for  sending  and  receiving  Semi- 
Wireless  telegrams  with  any  code;  and,  when  used  with  two  or  three  good 
dry  batteries,  we  absolutely  guarantee  that  it  will  send  and  receive  Semi- 
Wireless  messages  loud  and  clear  over  any  properly-built  line,  up  to  1,000 
miles .  in  length.  For  short  lines — up  to,  say,  500  feet — this  may  also  be 
used  to  telephone,  but  two  wires  should  be  used  for  the_  line  and  the  words 
should  be  spoken  loud  and  clear  directly  into  the  receiving-transmitter. 


ST.  J.  SEMI-WIRELESS- Continued 

The  _Standard  Cabinet,  No.  2552,  includes  the  Standard  Instrument, 
No.  2550,  and  two  batteries,  all  ingeniously  mounted  in  a  special  stained 
box  with  sliding  cover.  The  base  of  the  in- 
strument swings  in  and  out  of  the  box  upon 
pivots,  and  the  outfit  is  wired  and  ready  for 
immediate  use.  This  makes  a  splendid  outfit 
for  those  who  do  not  care  for  the  telephone 
part  of  the  system,  and  we  guarantee  that 
the  two  batteries  will  furnish  power  enough 
to  telegraph  loud  and  clear  over  the  longest 
line  you  will  ever  want  to  build. 

The  Loud-Talking  Long-Distance  Trans- 
mitter, No.  2554,  may  be  added  to  either 
No.  2550  or  No.  2552  at  any  time  to  make  a 
complete  long-distance  station  for  telegraph- 
ing and  telephoning,  connections  being  made 
as  shown  in  the  Book  of  Instructions.  The 
peculiar  construction  of  this  transmitter 
makes  the  results  very  unusual  on  all  ordi- 
nary lines.  This  transmitter  is  shown  near  the 
top  of  the  Portable  Set,  No.  2557,  mounted 


No.  2552 
upon  a  frame-work;  when  sold  as  No.  2554,  however,  it  is  neatly  mounted 


in  a  separate  stained  box  that  can  be  fastened  up  just  above  'the  Standard 
Instrument  or  the  Standard  Cabinet.  As  we  absolutely  guarantee  this 
transmitter  to  give  perfect  satisfaction  over  all  properly-constructed  lines 
lip  to  500  miles  in  length,  you  will  understand  that  for  all  of  the  ordinary 
lines  that  will  be  put  up  by  amateurs  the  results  will  be  more  than  satis- 
factory; in  fact,  you  will  be  astonished  at  the  way  these  peculiar  instru- 
ments respond  to  the  slightest  whisper. 

The  Standard  Cabinet  and  Transmitter  Outfit,  No.  2556,  provides  the 
same  instruments  as  are  furnished  in  the  Portable  Outfit,  only  the  tele- 
graph and  telephone  parts  are  mounted  in  separate  boxes  and  not  in  one 
large  box. 

Our  Portable  Set,  No.  2557,  is  making  a  great  hit — and  no  wonder.  This 
set  is  put  up  in  a  special  stained  box  with  handle  and  sliding  cover,  and  it 
stands  over  13  inches  high.  It  includes  the  standard  instrument,  No.  2550, 
and  the  loud-talking  transmitter,  No.  2554,  all  neatly  mounted  and  ready 
for  use.  You  can  connect  your  station  to  any  Semi-Wireless  line  in  one 
minute  by  passing  the  line-wires  through  the  eyeletted  holes  to  the  binding- 
posts  at  the  left.  When  you  consider  that  we  have  here  a  complete  tele- 
graph and  telephone  station  in  one — you  will  see  its  possibilities. 

When  we  tell  you  that  Semi-Wireless  messages  can  be  sent  loud  and 
clear  over  lines  1,000  miles  in  length,  we  are  only  hinting  at  the  capabilities 
of  this  wonderful  invention;  so  vou  need  not  fear  that  the  line  you  think 
of  building  may  be  too  long.  We  have  had  official  tests  made  of  Semi- 
Wireless  apparatus — the  hardest  tests  that  any  apparatus  could  have — and 
we  stand  ready  to  prove  every  claim  we  make.  With  its  ability  to  telephone 
and  telegraph  loud  and  clear  over  the  same  wire — and  a  small  cheap  wire 
at  that — without  the  use  of  dynamos  or  other  expensive  current-supply,  we 

invented.  You  can't  blame  our  customers  who  already  have  lines  for  being 
enthusiastic.  One  reports  that  he  can  hear  conversation  distinctly  six  feet 
from  the  receivers,  and  another  says  that  messages  are  readable  fifty  feet 
away.  We  could  tell  you  greater  things  than  this  about  Semi-Wireless,  but 
we  would  much  rather  confine  ourselves  to  things  that  can  be  done  by  any- 
one having  an  outfit. 

Learning  Wireless. — There  are  thousands  of  young  men  and  boys  who 
want  to  learn  wireless  and  general  telegraphy  and  who  can  not  afford  to 
buy  the  rather  expensive  outfits  that  are  needed  for  such  work;  and,  on 
the  other  hand,  many  young  men  do  buy  complete  wireless  outfits  and  then 
find,  to  their  surprise,  that  they  cannot  read  the  messages  because  they  are 
sent  so  fast  that  it  requires  a  great  deal  of  practise  to  make  them  out. 
Semi- Wireless  is  the  great  teacher  that  will  help  just  such  amateurs.  By 
having  several  students  on  the  same  line — and  there  can  be  fifty  as  well 
as  a  dozen — and  by  having  one  good  operator  to  teach  them,  the  whole 
line  can  be  instructed  at  the  same  time  and  rapid  progress  can  he  made  by 
all.  The  messages  can  be  sent  at  any  desired  speed  and,  if  the  operator 


ST.  J.  SEMI-WIRELESS-Om/V 

is  provided  with  the  leud-talking  trans- 
mitter, verbal  instructions  can  be  given 
to  all  at  the  same  time;  talks  can  be 
illustrated  by  actual  messages;  the  work 
can  be  made  most  practical.  Think  what 
a  blessing  such  instruction  will  be  to 
those  just  learning!  A  skilled  operator 
can  be  found  in  almost  every  town  who 
will  be  glad  to  give  this  instruction  at 
a  fixed  price  per  hour,  and  when  several 
share  the  expense  it  will  be  very  little 
for  each. 

As  the  messages  come  flying  through 
every  receiver  on  the  line  they  sound 
just  the  same  as  wireless,  and  where  the 
line  isn't  over  a  few  miles  long,  they 
can  be  heard  without  placing  the  receiv- 
ers to  the  ears.  This  system  is  a  great 
help  to  students  of  wireless  because  it 
gives  just  the  training  that  is  needed; 
and  to  crown  the  whole  thing,  Semi- 
Wireless  talks  as  well  as  it  telegraphs. 
You  may  be  getting  code  one  second 
and  talk  the  next,  so  what  more  could 
be  desired?  On  two- wire  or  belt  lines 
the  "calls"  come  in  so  loud  that  they 
can  be  heard  all  over  a  large  room. 

The  Greatest  Opportunity  Ever  Offered 
No.  2557  t0  StUdCnt8' 

MISCELLANEOUS  SEMI- WIRELESS  GOODS 


LIST 
No. 

NAME  OF  ARTICLE 

Price 

Postage 
Extra 

2501 
2505 

Coil    of    Insulated    Copper    Wire,    size    No.    24,    for 
inside  lines;  200  feet  with  50  double-pointed  tacks. 
Special     Galvanized     Steel     Line-Wire     for     outdoor 
lines.      Put   up   in    1,   2,    3J4    and    12-pound   coils. 
Lengths  given  are  approximate. 
1-lb.  coil,  308  feet   .          .                              

$0.25 
15 

$0.06 

2-lb.  coil,  616  feet  

.29 

3H-lb    coil    1078  feet                                    

50 

M 

5  }4   pounds,   1,694  feet    

.79 

t4 

1  00 

M 

9  pounds,  2,772  feet  

1.25 

44 

12-lb    coil    3  696  feet 

1  50 

€4 

\7y2  pounds,  5,390  feet  

2.25 

44 

2511 

2514 

2515 
1102 

Insulators,   made  of  hard   fibre;   allow  one  for  each 
50  ft.  of  line,  and  5  or  6  for  each  station. 
Semi-  Wireless  Insulators,   per   dozen  
Semi-Wireless     Testing-Switches     for     testing     and 
grounding  stations  to  locate  breaks,  etc.,  prepaid.. 
Clamp  for  grounding  wires  to  gas  or  water  pipes... 
Two-Cell   Battery-Sets    

.06 

.25 
.10 
.25 

.01 

.04 
.10 

1103 

Three-Cell  Battery-Sets                                            .    . 

35 

15 

2550 
2552 
2554 
2S55 
2556 

Cutting-  Pliers  for  line-wires,  etc  
Standard  Instrument,  as  per  cut,  each  station  
Standard  Cabinet,  as  per  cut,  each  station  
Loud-Talking,    Long    Distance    Transmitter  
Includes  one  each  No.  2550  and  No.  2554  
Includes  one  each  No    2552  and  No    2554 

.15 
2.00 
2.50 
1.50 
3.50 
400 

.05 

.15 
.25 
.15 
.30 
40 

2557 

Portable  Set,  as  per  cut,  each  station  
Must  be  sent  by  express;  weight,  5  Ibs. 

4.50 

HOW  TWO  BOYS  MADE  THEIR  OWN 
ELECTRICAL  APPARATUS 

By  THOMAS  fl.  ST.  JOHN,  Met.  E. 
Fifth  Edition  Price,  post-paid,  *i.oo 

This  book  contains  141  pages,  125  illustrations,  and  direc- 
tions for  making  152  pieces  of  apparatus.  Size,  5x7^;  red 
cloth. 

CONTENTS:  Chapter  I.  Cells  and  Batteries.— II.  Battery  Fluids  and  Solu- 
tions.— III.  Miscellaneous  Apparatus  and  Methods  of  Construction. — IV. 
Switches  and  Cut-Outs.— V.  Binding-Posts  and  Connectors.— VI.  Permanent 
Magnets.— VII.  Magnetic  Needles  and  Compasses.—  VIII.  Yokes  and  Arma- 
tures.—IX.  Electro-Magnets.— X.  Wire-Winding  Apparatus.— XI.  Induction 
Coils  and  Their  Attachments. — XII.  Contact  Breakers  and  Current  Interrupt- 
ers.— Xin.  Current  Detectors  and  Galvanometers.— XIV.  Telegraph  Keys  and 
Sounders.— XV.  Electric  Belte  and  Buzzers.— XVI.  Commutators  and  Current 
Reversers.— XVII.  Resistance  Coils.— XVIII.  Apparatus  for  Static  Electricity. 
—XIX.  Electric  Motors.— XX.  Odds  and  Ends.— XXI.  Tools  and  Materials. 

"  The  author  of  this  book  is  a  teacher  and  writer  of  great  ingenuity,  and  we 
imagine  that  the  effect  of  such  a  book  as  this  falling  into  juvenile  hands  must 
be  highly  stimulating  and  beneficial.  It  is  full  of  explicit  details  and  instruc- 
tions in  regard  to  a  great  variety  of  apparatus,  and  the  materials  required  are 
all  within  the  compass  of  very  modest  pocket-money.  Moreover,  it  is  system- 
atic and  entirely  without  rhetorical  frills,  so  that  the  student  can  go  right 
along  without  being  diverted  from  good  helpful  work  that  will  leaa  him  to 
build  useful  apparatus  and  make  him  understand  what  he  is  about.  The  draw- 
ings are  plain  and  excellent.  We  heartily  commend  the  book."— Electrical 
Engineer. 

"  Those  who  visited  the  electrical  exhibition  last  May  cannot  have  failed  to 
notice  on  the  south  gallery  a  very  interesting  exhibit,  consisting,  as  it  did,  of 
electrical  apparatus  made  oy  boys.  The  various  devices  there  shown,  compris- 
ing electro-magnets,  telegraph  keys  and  sounders,  resistance  coils,  etc.,  were 
1  the  instructions  given  in  the  book  with  the  above 
)  of  the  most  practical  little  works  yet  written 
r,  with  but  a  limited  amount  of  mechanical 
knowledge,  and  by  closely  following  the  instructions  given,  almost  any  elec- 
trical device  may  be  made  at  very  small  expense.  That  such  a  book  tills  a  long- 
felt  want  may  be  inferred  from  the  number  of  inquiries  we  are  constantly  re- 
ceiving from  persons  desiring  to  make  their  own  induction  coils  and  other 
apparatus.  "—Electricity. 

"  At  the  electrical  show  in  New  York  last  May  one  of  the  most  interesting 
exhibits  was  that  of  simple  electrical  apparatus  made  by  the  boys  in  one  of  the 
private  schools  in  the  city.  This  apparatus,  made  by  boys  of  thirteen  to  fifteen 
years  of  age,  was  from  designs  by  the  author  of  this  clever  little  book,  and  it 
was  remarkable  to  see  what  an  ingenious  use  had  been  made  of  old  tin  tomato- 
cans,  cracker-boxes,  bolts,  screws,  wire,  and  wood.  With  these  simple  mate- 
rials telegraph  instruments,  coils,  buzzers,  current  detectors,  motors,  switches, 
armatures,  and  an  almost  endless  variety  of  apparatus  were  made.  In  his  book 
Mr.  St.  John  has  given  directions  in  simple  language  for  making  and  using 
these  devices,  and  has  illustrated  these  directions  with  admirable  diagrams 
and  cuts.  The  little  volume  is  unique,  and  will  prove  exceedingly  helpful  to 
those  of  our  young  readers  who  are  fortunate  enough  to  possess  themselves  of 
a  copy.  For  schools  where  a  course  of  elementary  science  is  taught,  no  better 
text-book  in  the  first  steps  in  electricity  is  obtainable."— The  Great  Round 
World. 

THOriAS  M.  ST.  JOHN,  848  Ninth  Ave.,  New  York 


r 
j 


The    Study   of   Elementary 

Electricity  and  Magnetism 

by  Experiment 

By  THOMAS  M.  ST.  JOHN,  Met.  E. 

7HIRD  EDITION.  '  Price,  postpaid,  $1.25. 

The  book  contains  220  pages  and  168  illustrations.      It  measures 
5x7'/2  in.,  and  it  is  bound  in  green  cloth. 


CONTENTS:  Part  I.  Magnetism.— Chapter  I.  Iron  and  Steel.— II.  Mag- 
nets.— UI.  Induced  Magnetism.— IV.  The  Magnetic  Field.-V.  Terrestrial  Mag- 
netism. Part  II.  Static  Electricity.— VI.  Electrification.— VII.  Insulators  and 
Conductors — VIII.  Charging  and  Discharging  Conductors.— IX.  Induced  Elec- 
trification.—X.  Condensation  of  Electrification  —XI.  Electroscopes.— XII. 
Miscellaneous  Experiments.— XIII.  Atmospheric  Electricity.  Part  III.  Cur- 
rent Electricity.— XIV.  Construction  and  Use  of  Apparatus.— XV.  Galvanic 
Cells  and  Batteries.— XVI.  The  Electric  Circuit.— XVII.  Electromotive  Force. 
— XVm.  Electrical  Resistance.— XIX.  Measurement  of  Resistance.— XX.  Cur- 
rent Strength.— XXI.  Chemical  Effects  of  the  Electric  Current.— XXII.  Elec- 
tromagnetism.  — XXm.  Electromagnets.— XXIV.  Thermoelectricity.  —  XXV. 
Induced  Currents.— XXVI.  The  Production  of  Motion  by  Currents.— XXVIL 
Applications  of  Electricity.— XXVIII.  Wire  Tables.— Apparatus  List.-Index. 

This  is  a  text-book  for  amateurs,  students,  and  others  who 
want  to  take  up  a  systematic  course  of  electrical  experiments  at 
home  or  in  school.  It  will  give  a  practical  and  experimental 
knowledge  of  elementary  electricity,  and  thoroughly  prepare 
students  for  advanced  work.  Full  directions  are  given  for 

TWO  HUNDRED  EXPERIMENTS. 

The  experiments  and  discussions  are  so  planned  that  the 
student  is  always  prepared  for  what  follows.  Although  the  ex- 
periments may  be  performed  with  the  apparatus  that  is  usually 
found  in  school  laboratories,  the  author  has  designed  a  complete 
set  of  apparatus  for  those  who  want  to  have  their  own  outfit. 


If  you  want  to  take  up  a  systematic  course 
of  experiments — experiments  that  will  build  a 
lasting  foundation  for  your  electrical  knowl- 
edge—this book  will  serve  as  a  valuable  guide, 


Electrical  Apparatus  For  Sale 

A  COMPLETE  ELECTRIC  AND  MAGNETIC 
CABINET  FOR  STUDENTS,  SCHOOLS  AND 
AMATEURS.  SOME  EXTRAORDINARY  OFFERS 

This  Cabinet  of  Electrical  Experiments  contains  three  main 
parts:  (A)  Apparatus  ;  (B)  Text-Book  ;  (C)  Apparatus  List. 

(A)  The  Apparatus   consists  of   one  hundred  and  five   pieces, 
which  are  made  up  of  over  three  hundred  separate  articles  (see 
"Condensed  List").     The  outfit  is  ready  for  use  when  received, 
— a  few  simple  adjustments,  perhaps,  being  necessary.     This  set 
of  apparatus  can  be  used  over  and  over  again  for  years,  and  it  is 
in  every  way  practical  for  regular  laboratory  work. 

(B)  The  Text-Book— called   "The  Study  of  Elementary  Elec- 
tricity and  Magnetism  by  Experiment" — gives  full  directions  for 
two  hundred  experiments.    (See  Table  of  Contents.)    Price,  $1.25. 

(€}  The  Apparatus  List  is  an  illustrated  Detail-Book,  which  is 
devoted  entirely  to  this  special  set  of  apparatus. 

These  Outfits  have  been  of  gradual  growth,  as  they  are  the 
result  of  years  of  actual  work  with  students.  Changes  have 
been  recently  made  in  some  of  the  pieces,  and  in  placing  the  im- 
proved apparatus  upon  the  market  Mr.  St.  John  feels  that  he  is 
giving  a  great  deal  for  the  money. 

If  you  want  to  build  a  lasting  foundation  for  your  electrical 
studies,  you  will  find  this  course  of  experiments  of  the  greatest 
value. 

Offer  No.  I  :    Pieces  I  to  50 $1.00 

Offer  No.  4:    Pieces  51  to  105,  with   part  (C) 4.00 

Offer  No.  5:  Pieces  i  to  105,  with  part  (C) 5.00 

Offer  No.  6:  Complete  Cabinet,  parts  (A),  (B),  (C) 6.25 


Express  charges  must  be  paid  by  you.    Estimates  given. 


Special  Discount.  To  those  who  order  the  entire  outfit  at  one 
time  (Offer  No.  6)  the  special  price  of  (5.60  will  be  given.  This 
discount  of  65c.  will,  in  most  cases,  pay  the  greater  part  of  the 
express  charges. 

&  "  New  Special  Catalogue,"  which  pertains  to  the  above,  will 
jc  mailed  upon  application. 

THOnAS  M.  ST.  JOHN,  848  Ninth  Avenue,  New  York  City 


THINGS  A  BOY  SHOULD  KNOW 
ABOUT  ELECTRICITY. 

By    THOMAS    91.    8T.    JOHN,   Met.    1C. 

The  book  contains  180  pages,  and  260  illustrations;  it  measure! 
5 x  7/^  in.,  and  is  bound  in  cloth. 

Fourth  Edition  Price,  post-paid,  »!.««•> 

CONTENTS :  Chapter  I.  About  Frictional  Electricity.— II.  About  Magnets 
and  Magnetism.— III.  How  Electricity  is  Generated  by  the  Voltaic  Cell.— IV. 
Various  Voltaic  Cells.— V.  About  Push-Buttons,  Switches  and  Binding-Posts.- 
VI.  Units  and  Apparatus  for  Electrical  Measurements.— VII.  Chemical  Effects 
of  the  Electric  Current.— VIII.  How  Electroplating  and  Electrotyping  are 
Done.— IX.  The  Storage  Battery  and  How  it  Works.— X.  How  Electricity  is 
Generated  by  Heat.— XI.  Magnetic  Effects  of  the  Electric  Current.— XII.  How 
Electricity  Is  Generated  by  Induction.— XIII.  How  the  Induction  Coil  Works. 
—XIV.  The  Electric  Telegraph,  and  How  it  Sends  Messages.— XV.  The  Electric 
Bell  and  Some  of  its  Uses.— XVI.  The  Telephone,  and  How  it  Transmits  Speech. 
—XVII.  How  Electricity  is  Generated  by  Dynamos.  -XVIII.  How  the  Electric 
Current  is  Transformed.— XIX.  How  Electric  Currents  are  Distributed  for 
Use.— XX.  How  Heat  is  Produced  by  the  Electric  Current.— XXI.  How  Light 
is  Produced  by  the  Incandescent  Lamp.— XXII.  How  Light  is  Produced  by  the 
Arc  Lamp.— XXIII.  X-Rays,  and  How  the  Bones  of  the  Human  Body  are  Photo- 
graphed.—XXIV.  The  Electric  Motor  and  How  it  Does  Work.— XXV.  Electric 
Cars,  Boats  and  Automobiles.— XXVI.  A  Word  About  Central  Stations.— 
XXVII.  Miscellaneous  Uses  of  Electricity. 

This  book  explains,  in  simple,  straightforward  language,  many 
things  about  electricity;  things  in  which  the  American  boy  is  in- 
tensely Interested;  things  he  wants  to  know;  things  he  should 
know. 

It  is  free  from  technical  language  and  rhetorical  frills,  but  it 
tells  how  things  work,  and  why  they  work. 

It  is  brimful  of  illustrations — the  best  that  can  be  had — illus- 
trations that  are  taken  directly  from  apparatus  and  machinery, 
and  that  show  what  they  are  intended  to  show. 

This  book  does  not  contain  experiments,  or  tell  how  to  make 
apparatus;  our  other  books  do  that.  After  explaining  the  simple 
principles  of  electricity,  it  shows  how  these  principles  are  used 
and  combined  to  make  electricity  do  every-day  work. 


Everyone  Should  Know  About  Electricity. 

A.  VERY    APPROPRIATE    PRESENT 


REAL  ELECTRIC  TOY-MAKING 
FOR  BOYS 

•By  THOMAS  M.  ST   JOHN,  Met.  E. 

This  book  contains  140  pages  and  over  one  hundred 
original  drawings,  diagrams,  and  full-page  plates. 
It  measures  5  x  7^  in.,  and  is  bound  in  cloth. 
SECOND  EDITION  Price,  post-paid,  $1.00 

CONTENTS:  Chapter  I.  Toys  Operated  by  Permanent 
Magnets. — II.  Toys  Operated  by  Static  Electricity.— III.  Mak- 
ing Electromagnets  for  Toys. — IV.  Electric  Batteries. — V.  Cir- 
cuits and  Connections. — VI.  Toys  Operated  by  Electromagnets. 
VII.  Making  Solenoids  for  Toys. — VIII.  Toys  Operated  by 
Solenoids.— IX.  Electric  Motors.— X.  Power,  Speed,  and  Gear- 
ing.— XI.  Shafting  and  Bearings. — XII.  Pulleys  and  Winding- 
Drums.— XIII.  Belts  and  Cables.— XIV.  Toys  Operated  by 
Electric  Motors.— XV.  Miscellaneous  Electric  Toys.— XVI.  Tools. 
—XVII.  Materials. — XVIII.  Various  Aids  to  Construction. 

While  planning  this  book,  Mr.  St.  John  definitely  decided  that 
he  would  not  fill  it  with  descriptions  of  complicated,  machine- 
made  instruments  and  apparatus,  under  the  name  of  "Toy- 
Making,"  for  it  is  just  as  impossible  for  most  boys  to  get  the 
parts  for  such  things  as  it  is  for  them  to  do  the  required  machine 
work  even  after  they  have  the  raw  materials. 

Great  care  has  been  taken  in  designing  the  toys  which  are 
described  in  this  book,  in  order  to  make  them  so  simple  that 
any  boy  of  average  ability  can  construct  them  out  of  ordinary 
materials.  The  author  can  personally  guarantee  the  designs, 
for  there  is  no  guesswork  about  them.  Every  toy  was  made, 
changed,  and  experimented  with  until  it  was  as  simple  as  pos- 
sible; the  drawings  were  then  made  from  the  perfected  models. 

As  the  result  of  the  enormous  amount  of  work  and  experiment- 
ing which  were  required  to  originate  and  perfect  so  many  new 
models,  the  author  feels  that  this  book  may  be  truly  called 
"  Real  Electric  Toy-Making  for  Boys." 


Every  Boy  Should  Make  Electrical  Toys. 


Wireless  Telegraphy 

For   Amateurs   and    Students 

By  THOMAS  M.  ST.  JOHN,  Met.  E. 

The  book  contains  172  pages  and  over  one  hundred  and 
fifty  drawings  and  photographs;  it  measures  5x7^  in.; 
bound  in  cloth. 

SECOND  EDITION  Price,  post-paid,  $1.00 

CONTENTS:  Chapter  I.  Early  Methods  of  Wireless 
Telegraphy. — II.  Waves  in  Solids,  Liquids,  and  Gases. — III. 
Wave-motion. — IV.  Ether. — V.  Light  and  Light-waves.— VI. 
Action  of  Magnetism  through  Space. — VII.  Action  of  Static 
Electricity  through  Space. — VIII.  Action  of  Current  Elec- 
tricity through  Space. — IX.  The  Induction-coil. — X.  Electric- 
waves. — XI.  Oscillating  Currents. — XII.  Electric  Oscillators. 
— XIII.  Production  of  Electric-waves.— XIV.  Detection  of 
Electric-waves. — XV.  Experiments  with  Coherers. — XVI.  Ex- 
periments with  Decoherers. — XVII.  Electric-wave  Experiments. 
— XVIII.  Home-made  Coherers. — XIX.  Home-made  Auto- 
coherers. —  XX.  Anti-coherers  and  Other  Detectors. — XXI. 
Miscellaneous  Apparatus. — XXII.  Home-made  Accessories. — • 
XXIII.  Induction-coil  Experiments. —XXIV.  Aerials  and 
Grounds. — XXV.  Miscellaneous  Aids. 

This  book  is  designed  especially  for  students  and  others  who 
want  to  get  a  practical  and  theoretical  knowledge  of  wireless 
telegraphy,  and  for  those  who  want  to  experiment  without  being 
obliged  to  buy  the  expensive  apparatus  usually  required.  Full 
details  are  given  for  making,  at  small  cost,  nearly  everything 
that  will  be  needed. 

There  is  nothing  more  fascinating  than  wireless  telegraphy 
for  those  who  are  interested  in  scientific  subjects,  and  the  young 
man  or  boy  who  takes  it  up  from  an  experimental  standpoint — 
making  the  greater  part  of  his  own  apparatus — has  a  great  ad- 
vantage over  those  who  merely  have  information  from  books. 

Any  young  man  who  wants  to  get  at  the  root  of  the  matter  and 
build  up  a  solid  foundation  of  theoretical  and  practical  informa- 
tion will  find  this  book  a  great  help — no  matter  what  other  books 
he  may  have  upon  the  subject. 

It  tells  what  to  make  and  how  to  make  it;  what  to  use  and  how  to 
use  it;  and  besides,  it  u  full  of  practical  experiments,  directions, 
and  discussions. 


Electrical    Handicraft 

Containing  complete  directions  for  making  and  using  nearly  one 
hundred  and  fifty  pieces  of  electrical  apparatus,  including  various  devices 
and  outfits  for  experimental  purposes. 

By  THOMAS  M.  ST.  JOHN,  Met.  E. 

The  book  contains  252  pages  and  over  250  original  drawings  and  diagrams. 
Size,  5x7 }4  inches;  bound  in  substantial  cloth. 

Price,  post-paid,  $1.00. 

Contents  in  Brief:  Chapter  I.  Making  Permanent  Mag- 
nets.— II.  Magnetic  Needles  and  Compasses. — III.  Current 
Detectors  and  Galvanoscopes. — IV.  Handling  Metals. — V. 
Handling  Wood. — VI.  Binding-posts  and  Connecting  De- 
vices.— VII.  Switches,  Contact-points  and  Cut-outs. — VIII. 
Push-buttons  and  Strap  Keys. — IX.  Cores,  Yokes  and  Arma- 
tures.— X.  Machines  for  Winding  Electromagnets. — XI. 
Solenoids  and  Electromagnets. — XII.  Horseshoe  Electro- 
magnets.— XIII.  Apparatus  for  Measuring  Resistances. — 
XIV.  Resistance-boxes  and  Rheostats. — XV.  Current-reyer- 
sers  and  Pole-changing  Switches. — XVI.  Small  Electric-light 
Outfits.— XVII.  Small  Condensers.— XVIII.  A  "Handicraft" 
Workroom.— XIX.  Miscellaneous  Operations.— XX.  Tools 
and  Supplies. — Index. 

New  Ideas  in  Apparatus-making.  A  peculiar  system  of 
construction  has  been  invented  by  the  author  of  "Electrical 
Handicraft"  that  gives  unusual  results  and,  as  this  simple 
plan  has  been  used  throughout  the  whole  book,  home-made 
apparatus  can  now  be  produced  that  will  be  a  credit  to  any 
laboratory  and  give  new  interest  in  experimental  work. 

Plain  Directions.  Any  one  can  follow  the  plain  di- 
rections, aided  by  the  numerous  drawings  and  diagrams,  and 
make  good  practical  apparatus  that  is,  at  the  same  time,  fine- 
looking  apparatus;  in  fact,  some  who  have  seen  it  say  that  it 
is  home-made  apparatus  de  luxe  on  account  of  its  elegant  ap- 
pearance and  original  design. 

Inexpensive  Supplies.  The  best  of  it  all  is  this:  You  can 
get  materials  and  supplies  for  making  this  splendid  lot  of 
apparatus  for  very  little  money,  any  single  piece  costing  you 
but  a  few  cents.  Here  is  the  reason:  Nearly  all  of  the  sup- 
plies that  are  needed  for  this  out-of-the-ordinary  apparatus 
are  made  in  large  quantities  by  machinery  for  the  author's 
various  outfits — and  that  is  why  these  carefully  chosen  ma- 
terials can  be  furnished  at  so  low  a  price.  They  are  made 
as  they  should  be  made — metal  straps  nickel-plated,  and 
punched  if  you  like — and  so  the  result  is  a  happy  combination 
that  satisfies. 

It  is  with  much  pleasure  that  the  author  finally  places 
within  easy  reach  of  students,  amateurs  and  schools  a  line 
of  supplies  so  complete,  so  substantial  and  practical  and,  at 
the  same  time,  so  inexpensive. 

Send  for  "Electrical  Handicraft"  now,  so  that  you  can  be- 
gin this  most  fascinating  and  profitable  work  at  once. 


HANDICRAFT  TOOL  SETS 

HANDICRAFT  TOOL  SETS.  We've  had  a  lot  of  inquiries  about  tools 
to  go  with  these  new  ideas  in  apparatus  making;  and  as  the  methods  of 
construction  are  quite  unusual — in  fact,  absolutely  original — we  have 
decided  to  make  up  sets  of  tools  that  have  been  found  to  be  most 
useful.  While  ordinary  tools  are  needed  for  the  most  part,  a  few  spe- 
cial tools  are  essential. 

Time  and  energy  are  precious;  don't  waste  either  by  trying  to  make 
apparatus  with  poor  tools  or  with  tools  unsuited  to  the  work.  You  will 
get  the  best  value  if  you  buy  the  tools  in  sets. 

Note:  We  can  not  pay  express  charges  on  these  sets,  owing  to  the 
special  prices  given,  but  we  shall  be  glad  to  give  you  an  estimate  of 
the  charges  to  your  city  upon  application. 

TOOL  SET  NO.  2.  PRICE  $2.00.  One  Steel  Punch;  polished,  flat 
end. — One  light  Hammer;  polished,  iron,  nickel-plated;  hardwood  han- 
dle.— One  Iron  Clamp;  japanned,  2%-in.  opening. — One  Screw-Driver; 
tempered  and  polished  blade,  stained  hardwood  handle,  nickel  ferrule. 
— One  Vise;  full  malleable,  nicely  retinned,  lfi-in.  jaws,  full  malleable 
screw  with  spring. — One  File;  triangular,  good  steel. — One  File  Handle; 
good  wood,  brass  ferrule. — One  Foot  Rule;  varnished  woor,  with  English 
and  metric  systems. — One  Soldering  Set;  contains  soldering  iron,  sol- 
der, resin  and  directions. — One  Center-Punch ;  finely  tempered  steel, 
and  of  the  proper  size. — One  "St.  J."  Special  Eyelett inn-Tool ;  does 
fine  work  and  is  invaluable. — One  "St.  J."  Special  Combination  Hand- 
Drill  and  Winding-Machine;  takes  drills  up  to  and  including  three- 
sixteenths  inch;  finely  nickeled  and  finished  in  every  way;  strong  chuck 
and  hollow  handle  for  holding  drills.. — One  Special  Threaded  Spindle 
for  Winding-Machine.— One  Three-SIxteenths-Inch  Twist  Drill.— 
One  Drill-Point  for  small  holes.  These  straight-shank  drills  are  made 
of  the  best  steel,  properly  tempered. — One  Pair  of  Compasses;  for 
marking  circles  on  wooden  bases,  etc. — This  set  contains  16  tools. 

TOOL  SET  NO.  2%',  PRICE  $2.75.  This  set  contains  all  that  is  in 
No.  1J4  set,  together  with  the  following:  One  Pair  of  Pliers;  6  in. 
long,  bright  steel,  flat  nose,  with  two  wire-cutters;  practically  unbreak- 
able and  very  useful. — One  Pair  of  Tinner's  Shears;  cut  2&  in.,  hard- 
ened iron,  suitable  for  light  work. — One  Try-Square;  6  in.  blued  steel 
blade,  marked  in  one-eighth-in.  spaces. — One  Anvil;  polished  top  with 
japanned  body;  very  necessary  for  rivetting  and  eyeletting.  This  set 
contains  20  tools. 

TOOL  SET  NO.  3y4;  PRICE,  $3.75.  This  set  contains  the  same 
number  of  tools  as  Set  No.  2J4,  the  difference  in  price  being  due  to  the 
superior  quality  of  five  of  the  tools  which  replace  those  in  the  cheaper 
set.  These  five  tools  are:  (1)  Soldering  Set,  (2)  Vise,  (3)  Tinner's 
Shears,  (4)  Compasses,  (5)  Hammer.  The  Soldering  Set  is  larger, 
so  the  soldering  iron  holds  the  heat  better  than  the  smaller  one,  and 
this  is  a  great  help.  The  Vise  is  much  larger  and  heavier  than  the 
tinned  vise,  and  it  is  of  superior  quality,  with  strong  polished  jaws 
and  steel  screw;  body  nicely  japanned.  The  Tinner's  Shears  are  made 
of  fine  steel,  properly  tempered;  cutting-blades  polished,  thoroughly 
reliable.  Steel  shears  can  be  sharpened  when  they  get  dull.  The  Com- 
passes are  adjustable  with  screw  and  they  lock  in  place;  nickel-plated 
and  of  superior  quality,  with  pen,  pencil  and  two  sharp  points. — The 
Hammer  is  made  of  cast  steel,  weight  about  one  pound.  20  tools. 


Handicraft  Tool  Sets— (Continued) 

TOOL  SET  NO.  4y4;  PRICE,  $4.75.  This  set  is  most  complete, 
containing  nearly  everything  that  is  in  the  other  sets,  together  with  a 
number  of  very  useful  tools. — One  Steel  Punch;  polished,  flat  end.-— 
One  Steel  Punch,  for  punching  larger  holes.— One  Light  Hammer,  pol- 
ished, nickel-plated;  hardwood  handle;  proper  weight  for  nailing  bases. 
—One  Cast  Steel  Machinist's  Hammer;  ball  pein  and  of  fine  quality; 
proper  weight  for  punching  metal  straps,  etc. — One  Iron  Clamp; 
japanned,  2^4  in.  opening. — One  Large  Iron  Clamp. — One  Screw- 
Driver;  tempered  and  polished  blade,  stained  hardwood  handle,  nickel 
ferrule. — One  Ratchet  Screw-Driver;  great  help  and  saves  time  on 
some  work. — One  Small  Vise;  full  malleable,  nicely  retinned,  lfi-in. 
jaws,  full  malleable  screw  with  spring. — One  Large  Vise,  of  superior 
quality  for  larger  work;  strong  polished  jaws  and  steel  screw;  body 
nicely  japanned. — One  File;  triangular,  good  steel. — One  File  Handle; 
good  wood,  brass  ferrule. — One  Foot  Rule;  varnished  wood,  with  Eng- 
lish and  Metric  Systems. — One  Soldering  Set,  same  as  in  Set  No.  3ft. 
— One  Center-Punch;  finely  tempered  steel  and  of  the  proper  size. — One 
"St.  J."  Special  Eyeletting-Tool ;  does  fine  work  and  is  invaluable — 
One  "St.  J."  Special  Combination  Hand-Drill  and  Winding-Machine; 
takes  drills  up  to  and  including  three-sixteenths  in.;  finely  nickeled  and 
finished  in  every  way;  strong  chuck  and  hollow  handle  for  holding 
drills. — One  Special  Threaded  Spindle  for  winding-machine;  greatest 
possible  help  in  winding  cores. — One  Three-Sixteenths-Inch  Twist 
Drill. — One  Drill-Point  for  small  holes. — One  Pair  of  Pliers;  6  in. 
long,  bright  steel,  flat  nose,  with  two  wire-cutters;  practically  unbreak- 
able and  very  useful. — One  Pair  of  Tinner's  Shears;  made  of  fine 
steel  and  properly  tempered;  cutting  blades  polished,  thoroughly  relia- 
ble, sometimes  called  steel  "snips." — One  Try-Square;  6-in.  blued  steel 
blade,  marked  in  one-eighth-in.  spaces. — One  Pair  of  Compasses;  same 
as  in  Set  No.  3 ft,  with  adjusting-screw,  etc. — One  Anvil;  polished  top 
with  japanned  body;  very  necessary  for  ri vetting  and  eyeletting. — One 
Hollow-Handle  Tool  Set;  the  polished  hardwood  handle  holds  10  tools, 
including  gimlet,  chisel,  brad-awls,  etc. — One  Saw;  steel  frame,  polished 
pteel  blade;  useful  for  sawing  off  small  pieces  of  wood. — One  Pair  of 
Shears  for  cutting  paper  and  cloth  for  electromagnets,  etc. — This  set 
contains  28  tools  besides  those  in  the  hollow-handle  tool  set. 

SPECIAL  SIX-TOOL  SET;  PRICE,  $1.35;  PREPAID,  $1.80.     In  case 

you  are  well  supplied  with  ordinary  tools  and  want  only  the  special 
tools  needed  for  this  work,  the  following  outfit  will  be  a  great  help. 
This  special  set  contains:  One  "St.  J."  Special  Eyelettlng-Tool;  this 
tool  was  devised  by  Mr.  St.  John  after  considerable  experimenting  to 
produce  a  good  tool  that  would  be  cheap;  it  positively  does  as  good 
work  as  an  expensive  foot-power  machine;  simply  invaluable. — One 
"St.  J."  Special  Combination  Hand-Drill  and  Winding-Machine;  takes 
drills  up  to  and  including  three-sixteenths  in.;  finely  nickeled  and  fin- 
ished in  every  way;  winds  electromagnets  splendidly. — One  Vise  for 
clamping  the  "St.  J."  winding-machine  to  the  table;  this  is  the  tinned 
vise  with  li^-in.  jaws. — One  Special  Threaded  Spindle,  for  winding- 
machine;  used  in  winding  threaded  cores. — One  Three-Sixteenths-Inch 
Twist  Drill,  the  size  mostly  used  for  handicraft  bases. — One  Drill-Point 
for  small  holes. — This  special  six-tool  set  will  be  a  splendid  addition  to 
any  laboratory  or  workshop,  and  it  is  well  worth  the  price,  $1.35. 
We  will  send  this  set  by  mail  or  express,  prepaid  to  any  point  in 
the  United  States  for  $1.80. 


PLEASE    SEE   DIRECTIONS    FOR    SENDING    MONEY 


A  MOTOR  THAT  CAN  DO  THINGS 

The  "St.  J.  Motor  No.  1"  (List  No.  2201)  is  designed  for  students  and 
others  who  want  a  small  motor  for  experimental  purposes  as  well  as  for  all 
of  the  work  that  any  small  motor  can  do.  We  believe  this  to  be  the  best 
small  motor  made,  and  we  know  that  it  can  be  used  in  more  ways  than  any 
other  motor  of  equal  cost  ever  built.  It  has  four  binding-posts, — making  it  pos- 
sible to  energize  the  field  or  armature  separately, — and  so  it  can  be  used 
in  circuits  with  reversers  and  rheostats  for  experiments.  The  speed  and 
direction  of  rotation  can  be  changed  at  will,  thus  adapting  it  for  running 
toys,  etc.  As  the  binding-posts  are  mounted  upon  the  frame,  this  motor 
can  be  taken  from  the  base  for  remounting  and  using  in  many  ways,  and 
as  it  has  a  three-pole  armature  it  will  start  promptly  in  any  position.  The 
shaft  carries  a  pulley,  and  a  fan  can  be  added  at  any  time.  One  cell  will 
give  a  high  speed,  and  more  cells  may  be  added,  according  to  the  work  it 
has  to  do. 

Motor  No.  1  stands  3%  inches  high.  It  is  finished  in  black  enamel  with 
nickel-plated  trimmings, — strong  and  well  made.  With  it  are  furnished  three 
nickel-plated  connecting-straps,  which  are  to  be  used  for  connecting  the 


No.  2201 


field  and  armature  in  "series"  or  "shunt."  So  much  can  be  done  with  this 
motor  that  it  is  simply  impossible  to  tell  it  here;  in  fact,  it  is  used  as  the 
basis  for  a  whole  book  of  60  experiments  called  "The  Study  of  Electric 
Motors  by  Experiment,"  and,  when  used  in  connection  with  the  other 
parts  of  the  Motor  Outfits,  it  will  give  a  practical  knowledge  of  motors 
that  no  other  plan  can  give. 

These  motors  and  motor  outfits  have  been  highly  praised  by  electrical  ex- 
perts and  educators  as  being  invaluable  to  students.  They  can  do  every- 
thing the  big  motors  can  do,  and  if  used  with  the  rheostats,  reversers  and 
other  apparatus  in  the  outfits,  the  student  will  have  a  whole  motor  labora- 
tory. 

Why  not  get  a  motor  that  has  brains  and  that  can  do  tricks  and  experi- 
ments? Any  good  motor  will  go  when  you  turn  on  the  power;  but  that 
doesn't  mean  much  when  it  comes  to  understanding  things. 

No.  2201 — "St.    J.    Motor    No.    1,"    with    Wiring-Diagrams,    $1.00 
If  sent  by  mail,  postage  extra .15 


St.  J.  ELECTRIC  MOTOR  OUTFITS 

These  outfits  have  been  designed  for  students  and  others  who  want  to 
do  real  experimental  work  with  motors,  so  as  to  get  right  down  to  the 
bottom  of  the  matter  and  thoroughly  master  the  foundation  principles  of 
the  subject.  It  is  simply  astonishing  to  see  how  much  can  be  learned  with 
one  of  these  outfits,  especially  if  the  work  be  done  as  fully  detailed  in  "The 
Study  of  Electric  Motors  by  Experiment."  Every  electrical  laboratory 
should  have  one  of  these  sets,  and  the  more  you  know  about  motors  the 
more  you  will  appreciate  an  outfit  of  this  kind. 

Don't  simply  read  about  motors, — get  right  down  to  the  practical  part  of 
it  and  experiment  for  yourself.  Every  experiment  will  settle  an  important 
point  in  your  mind. 

No.  2224 — Electric  Motor  Outfit,  No.  \y2  contains: 

One   "St.   J.    Motor   No.    1,"    List   No.    2201 $1.00 

One  Five-Point  Rheostat,  No.    1724 25 

One  Double-Key  Current  Reverser,   No.   1728 25 

One  Set  of  Wires  for  Connections 02 

No.  2224— Complete,  as  above,  with  wiring-diagrams 1.50 

If  sent  by  mail,  postage  extra 20 

Two  dry  batteries  should  be  used  with  this  outfit,  but  they  are  not  in- 
cluded. We  use  our  Two-Cell  Set,  No.  1102,  costing  25c.,  postage  extra,  lOc. 

No.  2225 — Electric  Motor  Outfit,  No.  2,  contains: 

One  "St.  J.   Motor  No.   1"  complete,  No.  2201 $1.00 

One   Five-Point   Rheostat,   No.    1724 25 

One  Double-Key   Current  Reverser,   No.    1728 25 

One   Simple   Current  Detector,    No.    1501 10 

One  Two-Point  Switch,  No.   1062 05 

One  Nickel-Plated  Strap  Key,  No.   1083 06 

One  Magnetic  Needle,  in  box,  No.  1510 04 

One  Box  Iron  Filings,  No.   1351 02 

One   Set  of   Wires   for  Connections 02 

One  Copy  of  "The  Study  of  Electric  Motors  by  Experiment" 25 

No.  2225 — Complete  Outfit,  if  sold  together,  as  above $2.00 

If  sent  by  mail,  postage  extra 25 

Two  dry  batteries  should  be  used  with  this  outfit,  but  they  are  not  in- 
cluded. Our  Two-Cell  Set,  No.  1102,  costs  25c.;  postage  extra,  lOc. 


No.  2226 — Electric  Motor  Outfit,  No.  2y2,  contains: 

One  "St.  J.   Motor  No.    1"  complete,  No.  2201 $1.00 

One   Five-Point   Rheostat,   No.    1724 25 

One  Eleven-Point  Rheostat,   No.    1725 35 

One  Double-Key  Current  Reverser,   No.    1728 25 

One  Handy  Current   Detector,    No.    1502 15 

One  Two-Point  Switch,  No.   1062 05 

One  Nickel-Plated  Strap  Key,   No.   1083 06 

One  Set  of  Wires  for  Connections 02 

One  Box  Iron  Filings,  No.   1351 02 

One  Package  of  assorted  Iron,   Steel,   etc.,    10   pieces,   No.   1340 05 

One  Miniature  Electric  Lamp,  No.   2101 12 

One  Miniature   Receptacle,   No.   2121 05 

One   Magnetic   Needle,    No.    1510 04 

One  Copy  of  "The  Study  of  Electric  Motors  by  Experiment" 25 

No.  2226 — Complete  Outfit,  if  sold  together,  as  above,  only $2.50 

If  sent  by  mail,   postage  extra 30 

Three   dry  batteries  should  be   used   with  this   outfit  but  they   are   not  in- 
cluded.    Our  Three-Cell    Set,  No.   1103,  costs  35c.;  postage  extra,   15c. 


THE  STUDY  OF   ELECTRIC   MOTORS    BY    EXPERIMENT 

contains  Sixty  Experiments  that  Bear  Directly  upon  the  Construction, 
Operation  and  Explanation  of  Electric  Motors,  together  with  Much  Helpful 
Information  upon  the  Experimental  Apparatus  Required.  This  book  will 
be  a  great  help  to  those  who  want  to  do  real  experimental  work  with  mo- 
tors. It  contains  10  chapters,  110  pages,  over  70  illustrations  and  diagrams, 
and  you  can  not  afford  to  be  without  it. 

No.  R57P — The  Study  of  Electric  Motors  by  Experiment,  paper  cover,  $0.25 
No.  R57C — The  Study  of  Electric  Motors  by  Experiment,  bound  in  cloth,  .50 


RHEOSTATS  AND  REVERSERS 

These  ingenious   rheostats  are   made   in   two   sizes   for   experimental   pur- 

Coses,  and  they  are  most  useful  for  regulating  the  speed  of  motors,  the 
rilliancy  of  lamps,  etc.,  etc.  Some  small  rheostats  are  so  made  that  they 
change  the  current  too  gradually.  It  is  much  more  fun  to  have  the  motors 
leap  ahead  a  little  and  sing  a  different  tune  at  each  change  of  speed, — just 
like  the  big  motors  that  are  used  on  trolley  cars  and  for  power  purposes. 
These  instruments  are  made  with  nickel-plated  brass  straps,  binding-posts, 
contact-points,  etc.,  and  they  make  a  splendid  addition  to  any  electrical 
laboratory. 


No.  1728 


No.   1725 

The  Five-Point  Rheostat,  No.  1724,  measures  3j4x4j4  in.  It  is  designed 
to  regulate  the  speed  of  our  "St.  J.  Motor  No.  1"  when  running  with  two 
dry  batteries. 

The  Eleven-Point  Rheostat,  No.  1725,  measures  3^x6j4  in.  It  has  more 
resistance  than  No.  1724,  and  it  is  so  designed  that  it  can  be  used  with 
three  cells  for  our  small  motors,  and  also  for  experimental  work  with  minia- 
ture electric  lamp  outfits.  In  connection  with  our  small  lighting-plants  in 
which  the  current  is  generated  by  one  of  our  Dynamo-Motors,  No.  2209, 
this  rheostat  is  invaluable. 

No.  172-1 — Five-Point  Rheostat  (Postage  extra,  4c.)..$0.2S 
No.  172S— Eleven-Point  Rheostat  (Postage  extra,  5c.)     .35 

This  double-key  reverser  is  very  useful  for  experiments  with  motors,  etc., 
because  it  is  so  constructed  that  it  can  be  used  in  various  ways.  It  is, 
really,  a  key,  push-botton,  two-point  switch  and  a  reverser  combined,  so  it 
is  extremely  handy.  No.  1728  reverser  is  made  with  nickel-plated  brass 
straps,  binding-posts,  etc.,  all  parts  being  mounted  upon  a  neat  base 
measuring  2$4x3*/2  in. 

No.  1728 — Double-Key  Current  Reverser  (Postage  extra,  3c.)  $0.25 


This  diagram  is  one  of  many  contained  in  the  book  on  motors,  and  shows 
Motor  No.  1  shunt-wound  and  reversible,  using  rheostat  and  reverser  to 
secure  one  method  of  speed  control. 


University  of  California 

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405  Hilgard  Avenue,  Los  Angeles,  CA  90024-1388 

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